Abstract: In this paper,the Buff-breasted rat Rattus flavipectus was collected from the Hangzhou city,Zhejiang province.We used the lens weight to divide 893 speciemens into 4 groups:juvenile,subadult,adult and senior.The age structures of the population in October,1983 and 1988 were analysed.Several characters such as teeth wear,body weight and body length were also used to estimate the ages and were compared with lens weight.