Abstract: The acidity of precipitation in Guangzhou is studied.It points out that Guangzhou is acid-sensitive and the frequency for acid rain to take place is about 60 per cent in the urban area. Acidity of rain is strong in spring and weak in summer. Under stable weather conditions, such as inversion or breeze, acid rain is produced easily. Results of chemical analysis of rain sample show that effect of local pollution source is obvious on acid rain in the city.