The scale and pace of urbanization in China continue to increase at an unprecedented rate, and as a result, the intensity and extent of urban heat island effect increase. Based on MODIS and GIS data, the spatial and temporal characteristics of urban heat island effect in Chengdu and Chongqing are analyzed. The results show:(1) The urban heat island effect both in Chengdu and Chongqing were marked. The heat island intensity in Chengdu was 4.32 ℃, while that in Chongqing was 3.11 ℃. The land surface temperature (LST) of Chengdu increased from rural areas to center of the city, and that in Chongqing increased from southeast to northwest. (2) The heat island intensity in Chengdu and Chongqing was 4.32 ℃ and 3.11 ℃ in spring, respectively, which are much higher than those in other seasons. Additionally, the heat island intensity in Chengdu was stronger than that in Chongqing in most seasons. (3) During the last ten years, the scale of urban heat island effect increased both in Chengdu and Chongqing. The areas of strong and extremely strong heat island expanded, while the areas of weak and medium heat island reduced in Chengdu. On the contrary, the areas of strong and extremely strong heat island reduced, while the areas of weak and medium heat island expanded in Chongqing.