ABSTRACT:The aim of this experiment was to investigate the effect of supplementing the basal diet with oilseeds on blood parameters and composition of milk fatty acids, especially conjugated linoleic acid (CLA). Forty-eight lactating Holstein cows in early lactation were used in a randomized block design. The cows in each group were fed the control basal diet (the control diet) or diets containing roasted soybean (RSB), roasted linseed (RLS), roasted sunflower seed (RSS), hulled roasted peanut (HRP) and roasted cottonseed (RCS), respectively. Milk yield and dry matter intake (DMI) were not significantly different. Milk fat percentage and yield decreased (P < 0.05) in RLS, RSS and RCS diets compared with the control. Feeding various oilseeds had no effect on plasma parameters, but it tended to increase concentrations of trans C18:1 and C18:2 in plasma. In milk fat, the concentrations of short and medium fatty acids decreased while C 18 unsaturated fatty acids increased when the cows were fed oilseed diets. Cis-9, trans-11 CLA content increased (P < 0.01) in the milk fat of cows fed oilseeds. RSB treatment produced the highest (P < 0.01) content of cis-9, trans-11 CLA, which was a 60% increase compared with the control. The results indicate that the diets supplemented with oilseeds improve the content of C 18 unsaturated fatty acids and CLA in milk fat, and soybeans seem to be the optimal source to improve the nutritive value of milk compared with other oilseeds.