Abstract: Comprehensive observation of fog was conducted in Chongqing from Dec. 15 1989 to Jan. 15 1990 and from Dec. 7 1990 to Jan. 7 1991. In this paper, the physical and chemical characteristics of winter fog are analysed comprehensively. Some important characteristics of winter fog in Chongqing, which are different from fog of other areas in the country, are revealed.