Polyphenol oxidase (PPO) is a ubiquitous copper metalloprotein in many plants, PPO is encoded by multiple nucleicgenes, synthesized in cytoplasm , transferred into plastids in some forms , and then they become of enzyme activity. It is believed to be the primary factor for the quality of many crops. In this article, the research advances on existence, localization, molecular structure, physiological function, expression and regulation of Polyphenol Oxidase.