Based on daily air temperature data from 1957 to 2005, the difference in annual and seasonal air temperature trends between seven mountain stations and seven nearby urban stations in eastern China was investigated. The effect of urbanization on the variation trends of the mean air temperature, the maximum air temperature, and the minimum air temperature and the asymmetrical change of air temperature were also analyzed with the mountain stations as the background field. Results showed that the trends of the mean and minimum air temperatures were lager at the urban stations than at the mountain stations, while the trends of the maximum air temperatures were quite opposite. The air temperature trends for the urban stations showed asymmetrical characteristics more obviously than those for the mountain stations due to higher variation rates of the minimum air temperatures in the cities compared to those of the maximum air temperatures. The effect of urbanization was positive to the mean and minimum air temperatures, while negative to the maximum air temperatures. The effect of urbanization on the air temperature trends was asymmetric. The asymmetry of urban effect was the main cause for the asymmetrical change of air temperatures.