Poncirus trifoliata, an important rootstock of citrus crops, suffered from chlorosis in CaCO₃-rich soil,which is one of the difficult-to-tackle problems in the citrus industry in China. Experiments were conducted on the responses of calluses of Poncirus trifoliata to calcareous stress. Various stress levels were made by adding 0, 0.1%, 0.4%, 0.7%, and 1.0% CaCO₃ in MT medium. The results showed that the whole CaCO₃ stress caused poor ability of H⁺ exudation and low proliferation, weakened activity of peroxidese(POD) and decreased contents of active iron and soluble protein. CaCO₃ stress enhaced the activities of superoxide dismutase(SOD)and catalase(CAT)during the initial culture period and weakened it afterwards.,and enriched total iron for 25 days culture. The negative correlation between CaCO₃ concentration and the activities of POD, SOD, CAT, the content of active iron, the content of soluble protein and callus growth is signicant at the 0.01 or 0.05 level. The positive correlation between CaCO₃ concentration and medium pH is signicant at the 0.01 level.