The oxidation and the browning reaction of pyrogallol were caused by the polyphenoloxidase (EC 18.104.22.168) preparation obtained from the immature fruit of satsuma mandarin. The effects of some factors such as pH, temperature and inhibitors on this reaction were investigated. The optimum pH of this reaction was around 7.2-7.6, and no reaction was found below pH 6.0. This reaction was strongly inhibited by the compounds such as potassium cyanide and sodium diethyldithiocarbamate and also remarkably inhibited by L-ascorbic acid. The enzyme preparation was considerably stable at relatively high temperature.