Supported by RS and GIS, the land use change from 1982 to 2003 were analyzed and the impacts of land use changes on pH value, organic matter, total N, total P, total K, available N, available P, and available K in soil of Xiaojiang watershed, a typical karst agricultural region of Yunnan Province, Southwest China were assessed. The following aspects are concluded. (1) The total land use converted during the past 20 years in Xiaojiang watershed covers an area of 610.12 km², of which 134.29 km² of forestland was converted into cultivated land, and 210 km² of unused land was converted into cultivated land. (2) The rapid growth of population and the economic development were the main driving forces of land use change. (3) With the change in land use, the soil properties have been changed significantly. The pH, organic matter, total N, total P, total K, available N, available P and available K in soil in 1982 were 6.3, 38.02 g kg^-1, 1.86 g kg^-1, 1.63 g kg^-1, 10.94 g kg^-1, 114.42 g kg^-1, 11.65 mg kg^-1 and 64.69 mg kg^-1g, respectively; and those in 2003 were 6.73, 25.26 g kg^-1, 1.41 g kg^-1, 0.99 g kg^-1, 12.6 g kg^-1, 113.43 mg kg^-1, 11.11 mg kg^-1 and 151.59 mg kg^-1, respectively. Pared samples t-test of the tested indices of soil properties indicate that those indices have changed significantly during the last 20 years. But the soil properties changed differently, due to the differences in land use change. (4) Also, with the change in land use and management measures of soil, the modifications in soil properties which developed from carbonate rocks were more sensitive than those in the soil developed from sandstone.