Conjugated linoleic acid (CLA) is a collective term describing a mixture of positional and geometric isomers of linoleic acid with two conjugated double bonds. A considerable number of papers suggest anticarcinogenic properties of CLA, including their ability to suppress the growth of different cancer cell lines in vitro. The present research tendencies are focused on modification of CLA contents in numerous animal-derived food products, such as meat, eggs and butter. This is of a considerable practical significance, since functional food may be a preventive factor and aid treatment of many civilization diseases, including malignancies. The objective of the study was the investigation of the effect of lipids originating from egg yolk enriched with CLA isomers: cis9,trans11 and trans10,cis12 on proliferation of MCF-7 (ATCC Collection) mammary cancer cells. Egg yolk was enriched with CLA isomers in a natural manner, through feeding laying hens with a mixture of CLA isomers: cis9,trans11 and trans10,cis12 (4). The cells were incubated with lipids hydrolysate of egg yolk enriched with CLA isomers: cis9,trans11 or trans10,cis12, within the range of 0.12, 0.36 and 0.73 mg/ml for 24-72 h. There were no toxic effects of the hydrolysate on the cells as indicated by the Cytotoxicity Detection Kit (Roche). The results indicate that lipids of egg yolk with incorporated CLA isomers were more effective in inhibiting MCF-7 cell proliferation as compared to lipids originating from egg yolk without CLA enrichment.