The objective of this study was to determine the effect of adding vegetable oils (1.5% DM) to dairy cow rations on the content of unsaturated fatty acids in milk, including CLA isomers. The experiment was conducted on 16 Red-and-White cows in 4 × 4 Latin square design. The cows were divided into four groups and fed rations composed of grass silage, maize silage, spent brewer’s grain and concentrate. No significant differences were found in milk yield or the amount of standardized fat and protein content milk (FPCM). The addition of linseed oil significantly increased the milk fat content, while sunflower oil, significantly decreased it. Cows given rapeseed or linseed oil produced more fat than in the remaining groups. No significant differences were found in the protein percentage of milk or in milk traits (acidity, coagulability, density) among groups. Feeding cows rapeseed and sunflower seed oils increased the content of CLA isomers in milk by an average of 16%. The highest content of cis-9 trans-11 CLA isomers was found in the milk of cows receiving sunflower seed oil, the lowest, linseed oil. The daily production of cis-9 trans-11 CLA in milk ranged from 8.8 to 10.5 g/d.