Abstract: The browning degree，content of chlorogenic acid， catechin， epicatechin and polyphenol oxidase(PPO)activity with different substrates in fruits of five apple cuhivars were studied．The results indicated that the fruit with the highest browning degree was‘Fuji’apple llowed by ‘Starkrimson’．‘Orinn’．‘Jonagold’and‘Golden Delicious’．The total content of these three phenolic compounds was the highest in Starkrimson and Fuji apple fruits，and lowest in Golden Delicious．Catechin was deteched only in Jonagold and Golden Delicious fruits．Chlorogenic acid content was distinctively higher than epicatechin in Fuji apple fruit，while epicatechin higher than chlorogenic acid in Starkrimson and Orinn fruit．Taking chlorogenic acid as substrate，the fruit with the highest PPO activity was Starkrimson followed by Fuji and Golden
Delicious．Taking epicatechin as substrate，Fuji，Jonagold and Orinn fruits had higher PPO activity than Golden Delicious and Starkrimson．Taking catechin as substrate，PPO activity of Orin fruit was the highest followed by Fuji，and Starkrimson was the lowest．

Key words: Apple, Browning, Chlorogenic acids, Catechin, Epicatechin, Polyphenol oxidase activity