By taking Tianjin urban area as an example, a method is proposed to extract urban expansion by combining multi-temporal Landsat TM/ETM+ images and DMSP/OLS nighttime light data, and validated and analyzed. First, the candidate built-up area extent were obtained from DMSP/OLS data. Multitemporal Landsat TM/ETM+ images and derived multivariate textures of the obtained urban extent were classified to extract built-up areas for different dates. Urban expansions for different time intervals were obtained by post-classification comparison method. In addition, the thresholding method was applied to multitemporal DMSP/OLS nighttime light data to extract urban extents for different years and urban expansions of different time intervals were produced. The urban expansion results from DMSP/OLS data and urban statistical data were used to verify the Landsat TM/ETM+ results. The results demonstrate that the combination of Landsat data and DMSP/OLS data effectively reduce the spectral confusion between bare land and urban area and thus produce higher accuracy than useing spectral data from Landsat TM/TM+ images alone in extraction of urban built-up area expansion. Combination of Landsat TM/ETM+ data and DMSP/OLS nighttime light data provides an effective method for urban expansion extraction in mega-city areas.