Abstract: We had observed the ecology of the masked polecat ( Mustela cvcrsmanni ), and had measured the caloric values of its body digestibility and assimilation at Menyuan Horse-Breeder Ranch ( about 3250m in altitude), Qinghai Province from 1976 to 1981.The masked polecat is carnivore it blongs to secondary consumer in the alpine meadow ecosystems, and it is important on energe flow and material circulation.The food habits of the masked polecat were investigation by stomach content analysis, of which 73 stomachs were examined C tab. 1).The species is a typical carnivore, and its food consists almost exclusively of rodents, namely Ochctona curzon-iae, Myospalax fontanierii, Microtus oeconomus which were 86.0% of the total stomachs observed. The digestibility rate of masked polecat is 86.57±0.48%, the assimilation rate-78.61±0.48%.The masked polecat began to copulate in the Mar. -Apr., at this time the males were especially active.The reproduct only once a year, the litter size is generally two to eight, and averagely 5.25±1.25.One study plot which was chosen for obtaining a number of masked polecat in its typical habitats, was 58.253 hectares. The density was averagely has 0.1 animal per hectare.Caloric values of the animals body were 6.000±.066 kcal/g averagely for the whole year. and they were different during different seasons, namely 1.835±0.117; 1.699±0.087 and 2.16±0.059 kcal/g for the green up period ( Apr. to June ) Excuber-ance ( July to Aug. ) and Withering period ( Sept. to Nov. ) respectively ( tab. 4 ).