Abstract: Orange cv. luogan fruits from the market, were soaked with 200mg/L 2，4-D and 45% Sportak (a sterilant) for 3 mins . The fruits were coved with the pellicular bag, and then preserved at 25℃ and humidity 74％. The content of 2,4-D in fruit were determined by HPLC. The results shown that the 2,4-D content in fruit coat treated with 2,4-D for 12 h was higher than that in flesh (the control fruits). The endogenous content of 2,4-D level in flesh stored 5d after applying 2,4-D was promoted due to absorption 2,4-D came from fruit coat, and reached the highest and then decreased slowly ( 10 days). The endogenous 2,4-D content in flesh stored 30d after applying 2,4-D was 157.0.35 ng/g.FW, and less than 2000ng/kg in citrus fruit, which it is t2,4-D residue tolerance as the law from Ministry of Agriculture China demanded, so that the citrus from market was safe in flesh stored 30d treated with 2,4-D. 2,4-dichlorophenol hydroxylase is an important enzyme for 2,4-D degradation in plant; of which the activity was lower during the storage for 5 days and reached its maximum at the 30th day in flesh of orange cv. Luogan after 2,4-D treatment.