Based on a homogenized surface temperature dataset of 20 meteorological stations in Beijing, the urbanization effect on seasonal and annual daily minimum temperature, mean temperature and maximum temperature in Beijing during 1978-2008 is evaluated in this paper. The results show that for the annual minimum, mean and maximum temperatures, their spatial distributions show an increasing trend in Beijing area from north to south and from west to east, and there exists an obvious heat island for the annual maximum air temperature. This region is undergoing rapid increases in the minimum, mean and maximum temperatures. Regarding the minimum and daily mean temperatures the most affected stations are located in urban area and near suburban area, while for the maximum temperature the most affected stations are located in the middle zone from north to south in Beijing Area. The effect of urbanization on temperature increase is the most obvious in Beijing Observatory Station, followed by the effect on urban area stations and all the weather stations. In autumn, the urbanization effect on the minimum and daily mean temperature is more significant and in summer, the urbanization effect on maximum is more significant.