Exhibit 99.1

3050 Spruce Street, St. Louis, MO 63103 USA

Tel: (800) 521-8956 (314) 771-5765 Fax: (800) 325-5052 (314) 771-5757

FOR IMMEDIATE RELEASE -St. Louis, MO., July 26, 2011

SIGMA-ALDRICH (NASDAQ:SIAL) Q2 2011 SALES ACHIEVE NEW QUARTERLY HIGH. REPORTED SALES AND EPS INCREASE 15% COMPARED TO 2010. FULL YEAR 2011 DILUTED ADJUSTED EPS EXPECTATION

AFFIRMED AT $3.60 to $3.75.

HIGHLIGHTS:

2011 Results (all percentages are to comparable periods in 2010)

2011 Outlook (all percentages are compared to full year 2010 results)

CEO’s STATEMENT:

Commenting on second quarter 2011 performance, President and CEO Rakesh Sachdev said: “Our reported sales of $637 million set a new quarterly high. Adjusted diluted EPS of $0.93 for the second quarter of 2011 was consistent with our expectation. We have delivered solid performance with organic sales growth in our expected mid single digit range and a 15% increase in adjusted diluted EPS for the first half of the year. Our SAFC sales remained strong with a sequential increase over Q1 2011 levels

1

that resulted in 10% organic growth in this year’s second quarter versus the prior year. Strength in SAFC is being driven by continued strong demand for chemicals and precursors for semi-conductor and L.E.D. applications and for industrial cell culture media used for producing biological drugs. All of our Research business units grew sales organically in 2011’s second quarter and in line with our first quarter performance. We continue to benefit from our research initiatives in analytical chemistry, biology, traditional chemistry and materials science. This organic growth in research sales coupled with a 2% acquisition benefit helped achieve currency adjusted sales growth of 6% in our Research business in the second quarter.

We are very pleased with our continued strong growth in the emerging markets, as we posted a 20% organic sales growth in our focus markets of India, China and Brazil in the second quarter of 2011. In addition, we expanded our research product offering with the acquisition of Vetec Quimica Fina Ltda in Brazil. Vetec brings to Sigma-Aldrich more than 3,000 products and 30 years of expertise in the development, purification and packaging of high quality chemicals for laboratory and manufacturing applications, and adds to our ability to leverage the economies of producing and packaging products where our customers reside.”

Sachdev continued, “We have re-affirmed our organic sales growth expectation for 2011 in the mid-single digits. This organic growth, along with benefits from currency and acquisitions, are expected to drive overall reported sales growth to low double digits. We have also affirmed our diluted adjusted EPS outlook for 2011 of $3.60 to $3.75. As we integrate our new acquisitions, and continue to invest in new sales and profit growth initiatives, we remain committed to drive growth rates that outpace the underlying markets.”

2011 RESULTS:

Reported sales for the second quarter of 2011 of $637 million increased 15% from the second quarter of 2010. Excluding changes in foreign currency exchange rates and acquisitions that contributed 8% and 1%, respectively to sales growth, second quarter organic sales growth was 6%. Second quarter sales for the Company’s Research business grew organically by 4%, led by the Asia Pacific-Latin America region. Second quarter sales for the Company’s SAFC business achieved a new quarterly high, with an organic increase of 10% compared to 2010, led by double-digit growth in our Bioscience and Hitech products. A reconciliation of reported to adjusted organic sales is on page 8.

The operating income margin in the second quarter of 2011, excluding restructuring charges was 25.4% of sales compared to 26.2% of sales in the second quarter of 2010. Excluding the impact of changes in foreign currency exchange rates and the higher incremental amortization associated with our recent acquisitions, the operating income margin in the second quarter would have been 26.3% of sales, a 10 basis point improvement over 2010. During the quarter we spent an additional $3 million, or 50 basis points as a percentage of sales, in strategic spending on growth initiatives. Restructuring costs of $2 million were recorded in 2011’s second quarter related to the previously announced consolidation of certain manufacturing facilities in the U.S. and Europe. These restructuring actions reflect the Company’s efforts to improve operating efficiencies and lower our fixed cost structure as part of a longer term goal to improve operating margins.

The effective tax rate for the second quarter of 2011 was 28.5%, as forecast, compared to 30.7% in the second quarter of 2010. The lower tax rate in the second quarter of 2011 resulted from increased international tax benefits compared to the second quarter of 2010. The effective tax rate for all of 2011 is expected to be 29% to 30% of pretax income.

2

Free cash flow (defined on page 7) for the first half of 2011 was $210 million, comparable to that achieved in the first half of 2010. Higher net income was largely offset by a higher level of working capital and capital expenditures to support growth in the business. A reconciliation of net cash provided by operating activities to free cash flow is on page 9.

Other highlights from global sales growth initiatives include:

2011 OUTLOOK:

3

OTHER INFORMATION:

Cash Flow and Debt: Net cash provided by operating activities for the six months ended June 30, 2011 was $254 million compared to $247 million for 2010’s first half. Higher net income and non-cash charges in the first six months of 2011 compared to the same period in 2010 were largely offset by increases in accounts receivable and inventory. Capital expenditures in the first half of 2011 were $44 million compared to $37 million in 2010. Inventory levels increased to 6.5 months at June 30, 2011 compared to 6.0 months at June 30, 2010. This planned increase will enable us to enhance service and support the higher sales growth rates in the Asia Pacific-Latin America region. Free cash flow of $210 million for the first six months of 2011 was used primarily to return $65 million to shareholders through share repurchases and dividends, repay $23 million in debt and fund acquisitions of $75 million. The Company’s debt to capital ratio was 19% at June 30, 2011 compared to 21% at December 31, 2010. Total net debt (debt less cash and cash equivalents) at June 30, 2011 declined $117 since December 31, 2010.

Share Repurchases: 0.3 million shares were acquired during the first six months of 2011, all of which were repurchased in the first quarter of 2011. There were 122 million shares outstanding at June 30, 2011. The Company expects to continue to offset the dilutive impact of issuing share based incentive compensation with future repurchases. The Company may repurchase additional shares, but the timing and amount will depend upon market conditions and other factors.

Cautionary Statement: This release contains forward-looking statements relating to future performance, goals, strategic actions and initiatives and similar intentions and beliefs, including phrases “is expected”, “affirmed”, “to drive”, “to boost”, “to enhance” and other statements regarding the Company’s expectations, outlook, goals, beliefs, intentions and the like regarding future sales, earnings, free cash flow, share repurchases, acquisitions and other matters. These statements are based on assumptions regarding Company operations, investments and acquisitions and conditions in the markets the Company serves. The Company believes these assumptions are reasonable and well founded. The forward-looking statements in this release are subject to risks and uncertainties, including, among others, certain economic, political and technological factors. Actual results could differ materially from those stated or implied in this news release, due to, but not limited to, such factors as (1) global economic conditions, (2) changes in pricing and the competitive environment and the global demand for our products, (3) fluctuations in foreign currency exchange rates, (4) changes in research funding and the success of research and development activities, (5) failure of planned sales initiatives in our Research and SAFC businesses, (6) dependence on uninterrupted manufacturing operations, (7) failure to achieve planned cost reductions in global supply chain initiatives and restructuring actions, (8) changes in the regulatory environment in which the Company operates, (9) changes in worldwide tax rates or tax benefits from domestic and international operations, including the matters described in Note 10-Income Taxes-to the Consolidated Financial Statements in the Company’s Form 10-K report for the year ended December 31, 2010, (10) exposure to litigation, including product liability claims, (11) the ability to maintain adequate quality standards, (12) reliance on third party package delivery services, (13) an unanticipated increase in interest rates, (14) other changes in the business environment in which the Company operates, and (15) the outcome of the outstanding matters described in Note 11-Contingent Liabilities and Commitments-to the Consolidated Financial Statements in the Company’s Form 10-K report for the year ended December 31, 2010, (16)

4

acquisitions or divestitures of businesses. A further discussion of the Company’s risk factors can be found in Item 1A of Part 1 of the Company’s Form 10-K report for the year ended December 31, 2010. The Company does not undertake any obligation to update these forward-looking statements.

About Sigma-Aldrich: Sigma-Aldrich is a leading Life Science and High Technology company. Our biochemical and organic chemical products and kits are used in scientific research, including genomic and proteomic research, biotechnology, pharmaceutical development, and as key components in pharmaceutical, diagnostic and other high technology manufacturing. We have customers in life science companies, university and government institutions, hospitals and in industry. Over one million scientists and technologists use our products. Sigma-Aldrich operates in 40 countries and has 8,300 employees providing excellent service worldwide. We are committed to accelerating our Customers’ success through leadership in Life Science, High Technology and Service. For more information about Sigma-Aldrich, please visit our award winning web site at www.sigma-aldrich.com.

Non-GAAP Financial Measures: The Company supplements its disclosures made in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) with certain non-GAAP financial measures. The Company does not, and does not suggest investors should, consider such non-GAAP financial measures in isolation from, or as a substitute for, GAAP financial information. These non-GAAP measures may not be consistent with the presentation by similar companies in the Company’s industry. Whenever the Company uses such non-GAAP measures, it provides a reconciliation of such measures to the most closely applicable GAAP measure. See the Supplemental Financial Information on pages 8 and 9 for these reconciliations.

With over 60% of sales denominated in currencies other than the U.S. dollar, management uses currency adjusted sales growth when analyzing Company performance, and believes it is useful as well to investors, to judge the Company’s performance. Organic sales growth data presented in this release excludes currency and acquisitions impacts. The Company calculates the impact of changes in foreign currency rates by multiplying current period activity by the difference between current period exchange rates and prior period exchange rates, the result is the defined impact of “changes in foreign currency exchange rates”. While we are able to report currency impacts after the fact, we are unable to estimate changes that may occur later in 2011 to applicable exchange rates. Any significant changes in currency exchange rates would likely have a significant impact on our reported growth rates due to the volume of our sales denominated in foreign currencies.

Management also uses adjusted net income and EPS and adjusted operating income and operating income margins (reconciled on page 9) and free cash flow (defined on page 7), non-GAAP measures, to judge its performance and ability to pursue opportunities that enhance shareholder value. Due to the uncertain timing of future restructuring and other special charges, we are unable to include these charges in the 2011 diluted adjusted EPS forecast or provide a reconciliation to the corresponding GAAP measures. Management believes this non-GAAP information is useful to investors as well.

5

SIGMA-ALDRICH CORPORATION

Consolidated Statements of Income (Unaudited)

(in millions except per share amounts)

SIGMA-ALDRICH CORPORATION

Consolidated Balance Sheets

(in millions)

6

SIGMA-ALDRICH CORPORATION

Consolidated Statements of Cash Flows (Unaudited)

(in millions)

⁽¹⁾ Net cash provided by operating activities less capital expenditures.

7

SIGMA-ALDRICH CORPORATION

Supplemental Financial Information - (Unaudited)

Sales Growth by Business Unit

Business Unit Sales

(in millions)

8

SIGMA-ALDRICH CORPORATION

Supplemental Financial Information - (Unaudited)

Reconciliation of Reported Net Income to Adjusted Net Income

Income Statement Ratios

Reconciliation of Reported Operating Income Margin to Adjusted Operating Income Margin

Reconciliation of Free Cash Flow

(in millions)

9