Abstract: The authors in this paper have analysed statistically with respect to the variations at all seasons and among years of the relative fatness in gray hamster during 1968-1983. It was compared with house mouse(Mus muscu-lus L.)in the same region.The relative fatness of each animal was calculated by the following formula: K=100WW/L³.where K stands for the relative fatness,W the weight in grams,L the length of head and body in cms.Sexual difference with respect to fatness was observed, the female adults were fatter than the male adults.There were seasonal variations with respect to the relative fatness.The materials from the years 1972-1983 indicated the fatness of the gray hamst-er(K) was highest in autumn(October)and lowest during the summer (June to August),but from early winter(November)till next spring(April)the fatness was stable.The variations among years of the relative fatness in male adults showed that it had an obvious difference,but no correlation to its population density.The materials in October during 1968-1983 indicated that the fatness in gray hamster had very obvious correlation with the numbers of dominant species,house mouse(Mus musculus L.)in Taxihe,Manas county,Xinjiang Uygur Autonomous Region,the correlation coefficient r=-0.8212.