Four milking ewes (50±5 kg) were used in a 4 x 4 Latin square experiments to determine the effects of different sources and amounts of vegetable-origin fat in the diet on the fatty acid composition of milk. Ewes of the control group were fed a diet consisting of meadow hay and concentrate (60:40) that was supplemented for the experimental groups with rape seed oil, hydrogenated rape seed oil, or linseed oil at a level 4, 8 or 10% in dry matter of the diet. Addition of linseed and rape seed oil to the diet decreased (P < 0.05, P < 0.01) the level of total saturated fatty acids in milk. Rape seed oil and hydrogenated rape seed oil caused significant (P < 0.05, P < 0.01) increases in the level of mono-unsaturated fatty acids, whereas significant differences were not reached (P > 0.05) when linseed oil was fed to sheep. Also, the total amount of PUFA+MUFA increased in milk (P < 0.05, P < 0.01) when diets with linseed and rape seed oil were fed. The level of stearic acid differed depending on the added fat. A lower (P < 0.01) level of stearic acid was observed when 8% of linseed oil was added, whereas it was higher (P < 0.05) when 10% of linseed oil and 8% and 10% of rape seed oil were added to the ration. Feeding ruminants rations supplemented with fat of vegetable origin increased the energy content of the diet and also improved the level of desirable fatty acids in milk, e.g., MUFA and PUFA, which may be recommended in the treatment of some diseases.