Abstract: 138 rural stations are selected from all the 2300 observed stations located in the mainland of China,and the monthly mean temperature dataset from all the 614 national stations and 138 rural stations is tested for inhomogeneities and corrected. And, based on the adjusted dataset of the 614 national stations (i.e. the national basic/reference stations) and 138 rural stations, and the widely adopted gridweighted method for calculating regional average climate series, annual and seasonal averaged temperature series for the divided six regions in the mainland of China and China as a whole are constructed over the period 1961-2004, and an analysis of urbanization effect on surface air temperature changes observed from the national stations is conducted. The results show that, the increasing trend of annual mean temperature during the analysis period observed from national stations and rural stations is 0.278 ℃/(10 year) and 0.202 ℃/(10 year), respectively. Taking China as a whole, the annual mean temperature increasing trend induced by urbanization effect is 0.076 ℃/(10 year), accounting for 27.33% of the overall warming. As far as the six subregions is concerned, except for the northern Xinjiang, all the subregions show a significant urbanization effect on the surface air temperature increasing trend as recorded by the national stations during period 1961-2004.The regionaveraged annual urban warming, as is defined by the difference between the annual mean surface air temperature trend of the national stations and the rural stations, reaches 0.086 ℃/(10 year) in the middle and lower reaches of the Yangtze River and the Huaihe basin, accounting for 55.48% of the overall warming. The annual urban warming is estimated to be 0.060, 0.059, 0.042 and 0.042 ℃/(10 years), respectively, for the subregions of the Northeast and North China, the Tibetan Plateau, South China and the Northwest. And accordingly, the urban warming contribution to the overall warming is 55.48%, 23.23%, 23.20%, 15.35%, 13.73% and 1.57% for the subregions of the YangtzeHuaihe basins, the Tibetan Plateau,South China, the Northeast and North China, the Northwest and the northern Xinjiang, respectively. It is noticed that the small part of the selected rural stations can not represent the true rural background since they also suffered from the increasing urbanization and the results of urban warming presented here is underestimated to some extent. To sum up, the urbanization effect on the trend of the regionaveraged annual mean air temperature estimated from the national stations is dramatic, and it should be eliminated from the current regional surface air temperature series in order to make a more reliable dataset of background climate and thus improve the quality of detecting and monitoring of climate change.