Based on the monowindow algorithm of Qin et al. (2001,2003), the land surface temperature of Guangzhou City from Landsat/TM data and meteorological measurement data are retrieved, and the heatislandintensityindex and heatislandareas are calculated. The result shows that from 2000 to 2005, the urban heat island in Guangzhou is definitely increased with regard to the influences of initiative temperature, whole radiance flux and vegetation status. The heatislandintensityindexes on November 1, 2000, November 7, 2002 and November 23, 2005 are 1.15, 1.20 and 2.89, respectively. The heatislandareas on the above three days are 235.44 km2, 261.09 km2 and 381.42 km2, respectively. The main causes for the enhanced urban heat island in Guangzhou are the population increment and the enhanced greenhouse effect.