Abstract: This study is considered the first dealt with Trivers-Willard hypothesis in China using a wildlife population of plateau pikas (Ochotona curzoniae) by which we have investigated the relationship between maternal quality, litter sex ratio and litter size in a polytocous mammal. The results indicated that the reproductive time significantly affected the litter sex ratio. Although, the concentration of female adult plasma Immunoglobulin G (IgG) and Glucagon (Glu) at gestation, body weight, ear length, rear foot length and body length of adult female after gestation did not affect the litter sex ratio however, litter size has a significant negative impact on the litter sex ratio and body weight of adult females have a significant effect on the litter size. These results might give some evidence for the Trivers-Willard hypothesis in polytocous mammals.