Objective To study the effects of soy isoflavone on growth performance, meat quality and plasma antioxidant indexes of Wenchang chickens, and provide references for application of soy isoflavone in Wenchang chicken production.Method A total of 540 one-day-old Wenchang chickens were randomly divided into three treatments with four replicates per treatment and 45 chickens per replicate. The three treatment groups included the control group, antibiotics group and soy isoflavone group. The trial was performed in three stages including young, medium and old chicken stages.Result Growth performance results showed that the average daily gain(ADG), average daily food intake(ADFI) and feed gain ratio(F/G) were not significantly different among three groups from 1 to 30 days (P>0.05). ADG was significantly higher in soy isoflavone group than that in control group from 31 to 80 days (P<0.05). From 81 to 120 days, ADFI was significantly higher in soy isoflavone group than that in control group (P<0.05). Meat quailty results showed that meat color represented with L^*, a^* and b^*values and meat pH were not significantly different among three groups (P>0.05). Soy isoflavone group had a significantly higher cooked meat percentage than that of the control group(P<0.05). Analysis of the plasma antioxidant indexes showed that soy isoflavone group had significantly higher total antioxidant capacity (T-AOC) compared with antibiotics group from 31 to 80 days (P<0.05). From 81 to 120 days, creatine kinase (CK) activity was significantly lower in soy isoflavone group than that in antibiotics group, glutathione (GSH) content was significantly higher in soy isoflavone group than that in antibiotics group, and T-AOC was significantly higher in antibiotics and soy isoflavone groups than that in control group (P<0.05).Conclusion Dietary supplementation with 20 mg·kg^-1 soy isoflavone can increase ADG and antioxidantion of chickens from 31 to 80 days, dietary supplementation with 15 mg·kg^-1 soy isoflavone can increase ADFI, cooked meat percentage and antioxidant level of chickens from 81 to 120 days.