Abstract: The Populus ussuriensis seedlings were inoculated with four species of AM fungi, and we found that the mycorrhizal compounds could be formed by all the Glomus mosseae, G. intraradices, G. sinuosa and G. versiforrne. The taproot length and the ground diameter of inoculated seedlings were significantly different to the controls, so were the numbers of branch roots and the root biomass. The biomass accumulation of-seedlings was correlated significantly and positively to the infection.rate (P<0.05), which suggests that the P. ussuriensis is characterized by its dependence on the myeorrhization. The infection rate of G. mosseae and G. intraradices were 64.4% and 67.4% respectively. The volume and the total absorption area of root system were increased by inoculation with the AM fungi, especially for the active absorption region of that. The radicular active absorption region of seedlings inoculated with G. mosseae was 1.64 times of the controls. It is tested that the activity of the peroxidase in root system of inoculated poplars at the vigorous and final stage was much increased, while it was little decreased at the later stage as compared with the control treatments. The activity of the radicular polyphenol oxidase was much higher than the not colonized seedlings as effected by the AM fungi. This enzyme activity was highest when the poplar was growing vigorously, and the differences among the different inoculated ones were not