On the basis of Landsat images acquired in 1990, 2000, 2010, and 2015 and MODIS NDVI datasets acquired from 2010 to 2015, we analyzed urban expansion in Bangkok, including the spatio-temporal characteristics of built-up land, ecological-environmental effects (including vegetation greenness and land surface temperature), and the main driving factors of urban expansion. The results showed that (1) the built-up land areas in Bangkok has expanded continuously since 1990, showing a rapid-slow-rapid change trajectory. Urban expansion occurred mainly in the northeast direction and within the range of 14-20 km from the city center. The expansion patterns followed infilling pattern and edge-expansion pattern. (2) Urbanization affected vegetation greenness and heat island. Vegetation greenness declined overall, and a significantly decreased area was in the range of 10-20 km from the city center, which was in accordance with the main urban expansion area. Similarly, the spatial distribution of the heat island was coincident with urban expansion. The heat island increased overall, although local variations were less obvious. (3) Geographical conditions, social economy, and city layout were the main driving factors in urban expansion.