The age determination of Daurian Pika (Ochotona dauurica) plays a key role in the study of its population ecology. We analyzed the carcass weight of 198 samples of Daurian Pika (116 female, 82 male), captured in Abaga Qi, Xilinhot City, Inner Mongolia of China from 2009 to 2010, and found out that the average carcass weight of female and male pikas was significantly different (79.13±2.37 g vs. 91.76±3.74 g). Basis on the frequency distribution of each carcass weight, taking the reproductive status as a reference, we divided the female and male pikas into three age groups, juvenile, subadult and adult, respectively. The standard of carcass weight was juvenile (≤55 g), subadult (55-75 g), and adult (≥75 g) for female; juvenile (≤55 g), subadult (55-85 g), and adult (≥85 g) for male. The carcass weight between different age groups was significantly different and was also significantly positively correlated with body weight. Thus, the standard of age division by body weight resulted from the present study can be used as a potential tool in analyzing age structure in Daurian Pika population ecology study.