Abstract: The effects of different temperatures（36.3～39.3℃）on the secondary sex ratio and hatchability of muscovy were studied at the early stage of incubation.The results show that the difference of the sexual proportions of ducklings is significant（P<0.01）.The male proportion is increased while the female proportion is decreased with the increasing of temperature.When the incubation temperatures are from 36.3℃ to 37.3℃，the female proportion is the greatest and the rate ofmales to females is from 0.24 to 0.95，and if the temperatures is controlled between 37.8℃ and 39.3℃，the male proportion is much more than that of the female and the secondary sex ratio is from 1.39 to 5.38.The difference of the ratio of secondary sex to genetic sex does not exist（1:1，P>0.05）only when eggs are incubated at 37.3℃ and 37.8℃，but the differences exist at other temperatures（P<0.05 or P<0.01）.The correlation index between the secondary sex ratio and incubation temperatures of duckling is 0.99，and the range of predicted errors is from -34.88% to +14.58%.In some degree，regulating incubation temperature can control the secondary sex ratio of ducklings.Meanwhile，the incubation temperature obviously affects the hatchability of fertilized eggs.Within the range from 36.3℃ to 37.8℃，the hatchability is promoted as the temperature goes up，but from 37.8℃ to 39.3℃ it decreases.