Kefir has a unique microbial content that results in complex fermented milk drink. In this study, the antimutagenic power of acetone-extracted kefir was determined and compared to acetone-extracted yogurt and milk using different chemical mutagens in the Ames Salmonella microsomal test. Acetone extracts were fat portions of the kefir, yogurt and milk samples. The direct-acting mutagenic agents methylmethanosulphate (MMS) and sodium azide (SA), and the indirect-acting mutagenic agents aflatoxin B1 (AFB1), 2-aminoanthracene (2AA), and 3,2-dimethyl-4-aminobiphenyl (DMAB) were used in Ames test with TA 100 Salmonella typhimurium. Acetone-extracted fermented milk samples significantly inhibited mutagenicity for different percentages of MMS, SA, AFB1 and 2-AA. Results indicate that milk also had a lower antimutagenic effect. Additionally, the fatty acid profiles of milk, yogurt and kefir were determined. A two-step methylation method followed by gas chromatography was used to identify conjugated linoleic acids (CLA). Fermentation slightly affected fatty acid composition. Three isomers of CLA (c9, t11; t10, c12; t9, t11), butyric, palmitic, palmitoleic, oleic acids, which have been proven as antimutagenic components of milk fat, were in higher concentrations in kefir.