Isoperoxidases of fourteen species of poplars in Heilongjiang Province were analyzed by polyacrylamidegel disc-electrophoresis. The major zymogram of petioles of poplars was consisted of twelve kinds of isoenzymes, in which 35% zymogram was just the same and represented the specialized zymograms of poplars. The results of the experiments showed that the closer the affinity relationships of the species were, the greater the similar values between the zymograms were. There were very great similar values among natural hybrid species. But in sect.Tacamahaca Spach, the similar values betweenPopulus koreana Rehder andP. nakaii Skv. were obviously smaller. Isoenzyme analysis provided new information for plant classification on the molecular level.