Abstract:  Fall shoot of citrus （Citrus reticulata Blanco cv. Dahonggan） planted in Hanzhong City， Shaanxi Province， were cultured in Hoagland hydroponic solution and were used as experimental materials. The effects of different concentrations of H2O2 treatments on growth and physiological indexes of Dahonggan leaves under low temperature stress （4 ℃） were studied， in order to select the optimum concentration of H2O2 and to investigate the role of exogenous H2O2 in alleviating chilling injury of citrus to cold. It was shown that the degree of curl and cell membrane damage of Dahonggan leaf gradually increased with the extension of low temperature stress time. Both 0.1 and 1.0 mmol·L-1 H2O2 could ease leaves curling and wilting in Dahonggan caused by low temperature stress; however， the effect of 1.0 mmol·L-1 H2O2 was more significant than the concentration of 0.1 mmol·L-1 on alleviating damage of Dahonggan leaves caused by chilling stress. 1.0 mmol·L-1 H2O2 could obviously reduce the damage of cell membrane by lowering the increase of REC and MDA， reducing the accumulation of O.-2 and H2O2 and improving the activities of SOD and CAT in Dahonggan leaves under low temperature. Relatively high concentrations of exogenous H2O2 could not show alleviating effects; on the contrary， it produced some toxic effects.

Key words: Citrus reticulata Blanco cv. Dahonggan, low temperature stress, exogenous hydrogen peroxide, oxidative damage, alleviated effect