Abstract: The enzymology properties were studied on polyphenol oxidase in Saoguan Yam (Dioscorea fordii Prain et Burkill) by means of spectrophoto-metrically determining the activity at 410 nm with catechol as substrate, on the conditions of different pH,temperature and inhibitor concentration.The results showed that the optimum conditions were pH6.0 and temperature 40℃, and that Lascorbic acid, critic acid and NaCl all lowered the enzyme activity by inhibited the catalysis.