The present study demonstrated that supplementation of 1% OTP with different sizes had no significant effect on growth,while particle size affected the efficacy of dietary OTP in meat ducks. Fine but not coarse OTP decreased fat deposition andserum TG level. Our data also revealed that only fine OTP decreased drip loss of pectoralis major muscle and serum MDAcontent, and increased serum SOD activity. Therefore, fine OTP would be more effective in decreasing fat deposition andimproving meat quality and antioxidant activity in meat ducks