Characteristics of the urban heat island(UHI) effect of Nanjing and its cause are investigated by using the MODIS data in April 2004.The surface parameters from the MODIS data include surface temperature(t_s),albedo(α),and normalized difference vegetation index(NDVI).Their heterogeneities over urban and rural area are analyzed based on land cover classification,and their relations are also presented in order to explain the UHI effect.The results show that there exists obvious UHI effect.t_s over urban areas are 10.83% higher than those over rural areas,and NDVI and α over urban areas are by 62% and 18.75% less than those over rural areas,respectively.Surface temperature has significantly negative correlation with NDVI and their correlation coefficient is-0.73.Correlation between NDVI and albedo depends on spectrum of light.Difference in vegetation cover is the primary cause for UHI effect.