Abstract: The objective of this experiment was to evaluate the effect of ambient ammonia and humidity on antioxidant capacity and meat quality of broiler chickens. One hundred and ninety-two 21-day-old AA male broiler chicks were randomly allotted to two equal groups exposed to a high ambient ammonia (70 mg·kg^-1, H) and a low ambient ammonia (30 mg·kg^-1, L). Half of the broilers from each group were treated with relative humidity 60% (Control, C) and 35% (Treatment, T). Thus, four treatment groups named C+L, C+H, T+L and T+H, respectively. Growth performance of birds was recorded from 21 d to 42 d; The antioxidant capacity of blood and meat, meat quality were also determined. The results showed that average final BW, ADG, ADFI, T-AOC of blood and pectoralis muscle, and a^* value in pectoralis muscle at postmortem 45 min were significantly lower (P<0.05), while TBARS at postmortem 5 days, drip loss ratio, b^* value (P<0.05) and L^* value (P=0.054) at postmortem 45 min and shear force of pectoralis muscle(P=0.075) were increased when birds exposed to high level of ambient ammonia(70 mg·kg^-1) . Average final BW, ADFI (P<0.05), and ADG (P=0.072) as well as activity of SOD and GSH-Px in pectoralis muscle (P<0.05) and L^* value 45 min after slaughtering (P=0.053) were declined,while TBARS at postmortem 5 and 7 days and shear force of pectoralis muscle(P=0.057) were increased when birds exposed to low RH (35%) . Compared with C+L, the average final BW, ADG, ADFI, T-AOC of blood, activity of SOD and GSH-Px in pectoralis muscle, a^* value at postmortem 45 min were significantly lower (P<0.05),while TBARS at postmortem 5 and 7 days, drip loss ratio and shear force of pectoralis muscle were increased (P<0.05) when birds exposed to T+H. The results of this research suggested that high level of ammonia and low relative humidity in poultry house had adversely effects on growth performance, antioxidant capacity and meat quality of broilers，and the adversely effects of high level of ammonia could be enhanced under low relative humidity.