Abstract: Fruit sunburn rates of four citrus varieties such as‘Shatangju’，‘Gonggan’，‘Hongjiang’sweet orange and‘Anliu’sweet orange were investigated. Fruits were used as materials to find out the changes of antioxidant level. The results showed that the fruit sunburn rates were different in different citrus varieties. After fruit sunburned，superoxide anion was significantly accumulated in pericarp，lipoxygenase（LOX）activity and malondialdehyde（MDA）content significantly increased，leading to aggravation of cell membrane lipid peroxidation. Correspondingly，superoxide dismutase（SOD）activity，ascorbic acid（AsA）and glutathione（GSH）contents decreased significantly，peroxidase（POD）and polyphenoloxidase（PPO）activities were significantly enhanced. These results indicated that the epidermal antioxidant metabolism in fruit was disordered after fruit sunburned.

Key words: citrus, fruit, sunburn, antioxidant