Abstract: Using a data set of monthly mean temperature from 20 stations, the effect of urban heat island magnitude evolution on mean surface air temperature records of the last 40 years in Beijing region was analyzed. Two stages, a short cooling period between 1961-1969 and a significant warming period after 1969, were observed for both the urban and rural annual mean temperatures in Beijing area, and an obvious warming trend for each station is detected. The warming rate in winter is much higher than in any other seasons. It was also noted that the temperature anomaly series as calculated using the data from Beijing Station and the national basic/reference stations of the study area are significantly impacted by urban warming, especially for the last 20 years. Although the positive tendency of temperature anomalies is much greater in winter than in any other seasons, the urban warming is generally stronger in warm seasons. By analyzing the difference of rates of temperature changes between basic/reference stations and rural stations, we could further obtain the rate of warming induced by urbanization, and could calculate the relative contribution of urban warming to the total change in mean temperature. The contribution for annual mean temperature change of the basic/reference stations in Beijing area reaches to 48.5% for period of 1979-2000 and 71.1% for period of 1961-2000. It is also obvious that the contribution generally increases from winter and spring to summer and autumn. During 1961-2000, the recorded warming in summer and autumn can be entirely accounted for by the urbanization effect. Above all, these results indicate the essentiality to pay more attention to the effect of urban heat island magnitude change on long-term mean temperature series at least on regional scale.