Terms of the purchase have not been disclosed.
Sigma-Aldrich expects this acquisition to be neutral to earnings per share in 2012.
Research Organics will undergo transition into SAFC, the custom manufacturing and services business unit of Sigma-Aldrich.
Research Organics is a manufacturer of biochemicals for use in molecular biology, diagnostics, cell culture, pharmaceuticals, biopharmaceuticals, life sciences and biotechnology markets.
SAFC president Sigma-Aldrich executive vice president Gilles Cottier said: "This acquisition is an outstanding complement to our existing raw materials portfolio and will help us provide more innovative solutions for some of our customers’ toughest supply challenges."