Abstract: Polyphenol oxidase (PPO, EC 1.14.18.1 or 1.10.3.2) is responsible for the oxidative browning, loss of red color or nutrient quality. Increasingly more attention is received to characterize PPOs from various fruits and vegetables, as well as control their activity. In order to provide theoretical basis for technology of tomato processing, the properties of PPO from an extract of mature red tomato (Lycopersicum esculentum Mill. cv 918) fruit were studied in this paper using spectroscopy. PPO, with actechol as substrate, had an optimum pH at 6.0 and optimum temperature at 40℃. 88% of the activity was maintained after heating at 50℃ for 10 min. PPO exhibited activity toward monohydroxyphenols, dihydroxyphenols and trihydroxyphenols. Catechol might be the most effective substrate for the PPO, and the Kinetic parameters maximum velocity and Michaelis constant for it were 226.30 U/min and 6.00 mmol, respectively. The oxidation of catechol catalyzed by PPO was inhibited by ascorbic acid as well as β-mercaptoethanol and L-cysteine, and could be remarkably enhanced by sodium dodecyl sulfate-polyacrylamide.