To study the effects of biotin on the performance and blood biochemical parameters in early lactating cows, eight primiparous healthy Holstein cows were assigned randomly to four groups with two cows per group according to a replicated 4×4 Latin square design .The cows in control group (group A) were fed the basal diet and the cows in other groups were fed the basal diet supplemented with 20 (group B), 30 (group C) and 40 mg/d (group D) biotin, respectively. The results showed that: 1) milk yields in groups B, C and D were 1.69, 2.19 and 1.56 kg/d higher than that in the control group, respectively (P<0.05); 2) milk protein percentage was increased by supplementing botin and milk protein percentage in groups A, B, C and D were 2.77%, 2.96%, 2.89% and 2.86%, respectively. Milk protein percentage in group B was significantly higher than that in control group (P<0.05); 3) compared with control group, the serum glucose concentration in groups B, C and D increased by 5.23 (P<0.05）, 11.98 (P<0.05）and 14.71 mg/dL (P<0.01), respectively. The serum free fatty acid concentration in group D (196.82 μmol/L） decreased by 33.41 μmol/L than that in control group (230.23 μmol/L, P<0.05) and there were no significant differences among the other groups (P>0.05). These results indicated that dietary biotin supplement could improve the performance and milk quality of Holstein cows and the optimal level was 30 mg/d. ［Chinese Journal of Animal Nutrition, 2009，21(6）:853-858］