The purpose of this study was to investigate the effects of dietary zinc, manganese and phytase levels on growth performance, serum biochemical parameters and serum zinc and manganese contents of broilers, to explore whether dietary phytase can improve the absorption and utilization of zinc and manganese, so as to reduce the supplemental levels of zinc and manganese in diet. A total of 696 fourteen-day-old healthy Arbor Acres (AA) broilers with similar body weight were randomly divided into 6 groups with 12 replicates per group and 10 broilers per replicate. The experiment was based on a 2×3 two factors design, 2 levels of phytase (0 and 2 000 FTY/kg) and 3 levels of zinc and manganese combination (30 mg/kg zinc+40 mg/kg manganese, 60 mg/kg zinc+70 mg/kg manganese, 90 mg/kg zinc+100 mg/kg, respectivly), composed 6 kinds of diets. The experiment lasted for 28 days. The results showed as follows:1) dietary addition of phytase significantly increased the average daily gain of broilers during 14 to 28 days of age (P=0.001), significantly increased the average daily gain of broilers during 29 to 42 days of age (P=0.038), and significantly decreased the feed to gain ratio of broilers during 14 to 28 days of age (P=0.022). 2) Dietary addition of phytase significantly increased the activities of glutamic-pyruvic transaminase (ALT) and total superoxide dismutase (T-SOD) in serum of broilers (P=0.027 and P=0.037), and significantly increased the activities of glutamic oxalacetic transaminase (AST), creatine phosphate kinase (CPK) and manganese superoxide dismutase (Mn-SOD) in serum (P=0.003, P=0.001 and P=0.007). Dietary addition of zinc and manganese significantly decreased the serum urea nitrogen (UN) content in serum of broilers (P=0.041). The interaction of phytase with zinc and manganese significantly affected the activities of CPK and T-SOD in serum of broilers (P=0.010 and P=0.006). 3) Dietary addition of zinc and manganese significantly increased the serum zinc content in serum of broilers (P=0.033), and dietary addition of phytase significantly increased the serum zinc content in serum of broilers (P=0.047). To sum up, dietary addition of phytase can improve the growth performance and serum antioxidant enzyme activities of broilers. Dietary addition of zinc and manganese promote the protein synthesis. Dietary addition of phytase do not reduce the additive amount of zinc and manganese.