Abstract: Isoperoxidases of 26 species and 2 varieties, belonging to 5 sections of Populus, were analysed by means of polyacrylamide gel slab electrophoresis. Experimental evidences indicate that the zymograms of petioles are stable. Whole anodal isozymes may be divided into 5 groups; a.b.c.d.e. Every species of Populus shared the c group isozymes. The b group is limited within the section Leuce, and only in this section, the a group enzymes are absent. The d group is very complicated, and fully expressed the species-specificity. Base on their specific zymograms, it is easy to distinguish one species from the others, sometimes, we can characterize the varieties, even some clones. It seems that, in the course of morphological evolution of Populus, the divergence oftheir isoperoxidases also occurred.