This experiment was conducted to investigate the effects of mannanase transgenic corn on growth performance, carcass performance and blood physiological and biochemical indexes of broilers. A total of 480 one-day-old Arbor Acres (AA) broilers were randomly allocated to 4 groups, with 6 six replicates per group and 20 broilers per replicate. The four groups showed as follows: group Ⅰ, broilers fed non-transgenic corn without addition of mannanase as the control; group Ⅱ, broilers fed non-transgenic corn with addition of microbial mannanase at low dosage of mannanase activity (500 U/kg); group Ⅲ, broilers fed mannanase transgenic corn with low dosage of mannanase activity (500 U/kg); and group Ⅳ, broilers fed mannanase transgenic corn with high dose of mannase activity (5 000 U/kg). The trial lasted for 42 d. The results showed that the average daily gain of broilers aged of 42 days in groups Ⅲ and Ⅳ was significantly higher and the ratio of feed to gain was significantly lower than those in control group (P<0.05). Slaughter percentage, eviscerated percentage of broilers aged of 42 days in group Ⅳ were significantly higher than those in group Ⅱ and control group(P<0.05). No significant differences were observed among the 4 groups in blood physiological and biochemical indexes (P>0.05). It is concluded that diet added mannanase transgenic corn can significantly improve the growth and carcass performance of broilers, while has no significant effects on the blood physiological and biochemical indexes.