Abstract: In this paper, some data of pH in precipitation samples over urban area of Nanjing during the periods from November 1979 to July 1980,is given. The result shows that the values of pH vary from 4.10 to 7.93,with mean value 5.62. Acid rains appear in January and July 1980,the mean values of pH are 5.52 and 5.26 respectively. The result is compared with the results of observations in Japan, England and United States of America.