The experiment was conducted to investigate the effects of lactobacillin on serum biochemical indices and antioxidant function in broilers. A total of 300 one-day-old broiler chickens were randomly divided into five groups with four replicates per group and 15 chickens per replicate. The chickens in control group (group Ⅰ) were fed with a basal diet, those in group Ⅱ were fed with the basal diet supplemented with antibiotics, and those in the other groups (groups Ⅲ, Ⅳ and Ⅴ) were fed with the basal diet supplemented with 50, 100 and 200 mg/kg lactobacillin, respectively. The experiment lasted for 70 days. The growth performance, serum antioxidant indices and biochemical parameters were measured on the 28th day and the 70th day of the experiment, respectively. The results showed as follows: 1) comparing with group Ⅰ, weight gain of broilers in groups Ⅱ to Ⅴ was significantly increased and feed/gain was significantly decreased on the 28th day (P<0.05), and weight gain of broilers in groups Ⅱ and Ⅳ was significantly increased and feed/gain in groups Ⅱ to Ⅴ was significantly decreased on the 70th day (P<0.05). Feed/gain in group Ⅳ was significantly lower than that in the other groups (P<0.05), while there were no significant differences in that among groups Ⅱ, Ⅲ and Ⅴ (P>0.05). 2) There was no significant difference in serum urea nitrogen content of broilers in all groups (P>0.05). Compared with group Ⅰ, the serum cholesterol content of 28-day-old broilers and alkaline phosphatase activity of 70-day-old broilers in groups Ⅱ to Ⅴ were significantly increased (P<0.01 or P<0.05), and the serum total protein content of 28-day-old broilers in groups Ⅱ and Ⅳ was significantly increased (P<0.05), but there were no significant differences in the contents of total cholesterol and total protein in serum of 70-day-old broilers among all groups (P>0.05). There were no significant differences in above all biochemical indices among groups Ⅱ to Ⅴ (P>0.05). 3) At 28 days of age, the serum SOD activity of broilers in groups Ⅱ and Ⅳ was significantly higher than that in groups Ⅰ and Ⅴ (P<0.05), but there was no significant difference compared with group Ⅲ (P>0.05); the serum T-AOC in groups Ⅱ to Ⅴ was significantly higher than that in group Ⅰ (P<0.01), but there was no significant difference among groups Ⅱ to Ⅴ (P>0.05). At 70 days of age, the serum SOD activity and T-AOC of broilers in groups Ⅱ to Ⅳ were significantly higher than those in group Ⅰ (P<0.01 or P<0.05), but there was no significant difference among groups Ⅱ to Ⅳ (P>0.05). In conclusion, dietary lactobacillin can improve growth performance and antioxidant function of broilers, and the suitable supplemental level in diets is 100 mg/kg.