The degradation of MC-LR in water by UV/H2O2 process was investigated. The effects of intensity of UV radiation, initial concentration of MC-LR, dosages of H2O2, initial pH value and anions on degradation of MC-LR by UV/H2O2 process were studied. The results show that the removal of MC-LR only by H2O2 is nearly zero, and UV process can degrade MC-LR to a certain extent. However, the degradation efficiency of UV/H2O2 process is much higher than UV and H2O2 process due to the synergetic effect between UV and H2O2. The removal of MC-LR increases with the enhancement of intensity of UV radiation, but decreases gradually with the increase of initial concentration of MC-LR. When the dosages of H2O2 change from 1 mmol/L to 3 mmol/L, the constant of degradation rate rises from 0.0844 to 0.1664. The optimum pH value is 3.13. The added anions have adverse effect on the degradation of MC-LR, especially carbonate and nitrate ions have the biggest influence among the studied anions.