Thirty high yielding dairy cows were used in experiment which was conducted to evaluate the effect of lupin seeds (Lupinus albus, var. Amiga) as a substitute for soybean meal in a diet. Cows were divided into three well balanced groups (K, P30 and P50), in a 3 x 3 Latin square design. The control diet (K) contained as a main source of protein extracted soybean meal, in P30 and P50 were replacements 30% and 50% of lupin seeds, respectively. Each period of the experiment lasted four weeks. First three weeks were acclimation period and at fourth experimental week the samples of milk, rumen fluid and blood (from tail vas) were taken. There were no statistically conclusive differences (P>0.05) in dry matter intake, milk production, milk composition, and basic parameters of blood and rumen fluid. We concluded that lupin seeds can effectively replace as much as 50% of soybean meal in a diet of dairy cows while maintaining the same level of milk performance.