By taking samples of for acidified waters and three contrast waters at outskirts of Chongqing City, chemical characteristics of typical acidified waters in southwest China were investigated. K+ , Na+, Ca-2+ and Mg-2+ are correlated significantly with pH. The change of total concentrations of Ca-2+ and Mg-2+ with time is consistent with that of pH. Mg-2+ and Ca-2+ played the significant role in buffering active H+ , and changes of K+ and Na+ from rainwater to waters were not significant. There is a linear relationship between logarithm of Al-3+ concentration and pH. In the acidified waters, there are high SO-4-2- and NO-3- contents. Sulfate in two typical acidified waters was about 1/3 from rainwater and 2/3 from dissolution of the soil around the waters, and nitrate was mainly from dissolution of the soil, because of a great amount of sulfate and nitrate had been accumulated in the soil. From correlation analyses among organic nitrogen or carbon and pH, DON, POC and DOC are positively correlated with pH, therefore organic substance do not cause the increase of active H+ content. The causes of the acidification of the waters are concluded mainly from acid precipitation and weak buffering capacity of the water environment.