Aerosol samples of PM2.5 were collected from 1 January to 31 January and 6 February to 24 February 2008 in Guangzhou. The concentrations of organic carbon, element carbon, watersolubility ions of all particle samples were obtained by chemical analyses. Ambient light extinction coefficients were calculated by IMPROVE visibility formula. The results indicated that the average mass concentration of PM2.5, OC, EC, watersolubility ions was 890±53.4, 16.9±11.9, 5.9±3.4, and 43.9±23.5 μg·m-3, respectively. The averaged value of extinction coefficient was 342±185 Mm-1 in winter. The major contributors to ambient light extinction coefficients included (NH4)2SO4(36.3%), NH4NO3(14.5%), POM(26.6%), EC(17.4%), and NO2(5.2%), respectively.