Abstract: Radiation fog was observed in Jinghong, Mengyang and Mengmai for 28 days from Dec. 26,1986 to Feb. 18,1987.A tri-ombination dropsize spectronteter was used for samplimg fog spectra, and GZW-1 type low altitude radio-sondes were used to obtain the vertical tomperature profile in the boundary layer. In order to know the distribution of fog and temperature in the mountain region, an observing car was used 77 times along the twisty road between Jing-hong and Mengyang to get data, with sampling interval of 1 km. With these observed data and historical records in local meteorologcal stations, the time-space distribution, temperature srratification and micropliysical structure of radianon fog in Xishuangbanna have been analysed, and some important characteristics about the fog's evolution have been obtained.