Abstract: Studies on the mammal ecology had been undertaken from May, 1982 to July, 1983 in Beijing. This paper deals with the characteristics of mammal fauna and eco-geography only.Beijing is located in the northwest of North-China plain, and its mountain area accounts for 62%.The following aspects have been attained. 1. Characteristics of mammal fauna (1) The species are poor in Beijing and unevenly distributed, with a total number of 41 species.(2 ) None of the species are out of the ordinary. The whole fauna is a mixture of the fauna of South China, North China, Inner Mogolia-Xin-jiang and the Pacific monsoon area.( 3 ) Human's economic activities have led to distinct changes of the fauna.2. Characteristics of the Eco-geographyAccording to the composition character of the rodent community and environment, eight types of Eco-geography can be formed.3. The mammal resourses, natural protection as well as rodent damage and population growth were discussed.