This paper studies the changes of isoenzymes and activities of pero-xidase(POD),and the relative role of every POD fraction during black tea pro-cess by means of polyacryamide gel electrophoresis and enzyme acivity measu-rement, resulted in proving that there was remnant POD activities in made blacktea. Morever, it discusses the use of 0.2M citric acid buffer (pH 5.6) toadjust the activities of POD, polyphenol oxidase (PPO) and their ratio in fer-men...