Abstract: pH has important effects on aquatic organisms and element cycling in lakes. The south part of the middle and lower reaches of the Yangtze River is one of the centers of acid rain in the world. The effects of acid rain on lake pH were studied through field investigation and simulated experiment. In the 68 investigated lakes along the middle and lower reaches of the Yangtze River, lake pH had a significant positive correlation with water temperature, dissolved oxygen and chlorophyll a, and a significant negative correlation with total nitrogen, nitrate, dissolved inorganic carbon and turbidity; the average pH value of lakes in acid rain areas was significantly lower than that in non-acid rain areas (P < 0.05). The results of the simulated experiment show that the pH value of the low trophic treatment (L) was lower than that of the high trophic treatment (H), and the increasing rates of pH in L treatment was slower than that in H treatment after the single addition of acid rain (pH=2.5, 4.0 and 5.0). The differences of the pH values with three pH treatments of acid rain decreased over time in both L and H treatments. The daily variations of the pH values with different treatments showed the same trend. At the end of the experiment, the pH values with acid rain addition and no acid rain addition had no significant difference in the two trophic treatments. The study indicates that although the increase of the content of chlorophyll a in lakes caused by eutrophication can enhance the buffer capacity to the acid rain, the persistent acid rain could have a potential impact on pH, aquatic organisms and biogeochemical cycles in lakes of this area.