Abstract: Tow polyphenoloxidase isozymes (ppo A and B) in crude extract from populus deltoides 1-69 bark were purified by ammonium sulfate fractionation. Sephadex C- 100 and DEAE-cellulose column chromatography to homogeneity. The data showed that final purification of ppo A and B obtained were 6. 7 and 5. 9 fold. Photographs ofpolyacrylamide dise gels stained with 0. 03 m catechol and 2% coomassie blue R-250 after electronphoresis of ppo A and B preparation showed single band, respectively. Molecular weight of ppo A and B determined by sodium dodecy 1.sulfate polyacryamide get electronphoresis was 38900 and 33000. From the amino acid composition, it was found that ppo A molecular contanied most large amounts of lysine (residue 86), least amounts of arginine (residue 3) and did not contain tyrosine, and proline, ppo B molecular contained largest amounts of serine (residue 37), least amounts of arginine (residue 3) and did not contain tyrosine. The ppo A and B gave pH optima of 6. 4 and 7. 0 and temperature optima of 50 C and 45 C.Thermostability of ppo A was relatively stable as compured with ppo B. Of a number of phenolic compound tested, Km value of ppo A and B for catechol was least (0. 39 and 0. 34 mM), they had largest affinity for catechol. Therefore, ppo A and B was catecholase. In a number of compound tested, 1mM L-systein, sodium thiosulfate, thiourea, sodium dithyldithiocarbamete, sodium chloride and sucrose produced an inhibiting effect on activity of ppo A and ppo B, 0.1mM sodium chloride and sucrose caused promotive effect of activity of ppo B.