Several factors affecting on transformation efficiency were studied to establish a Agrobacterium rhizogenes mediated system for the transformation of Populus species, and We could obtaine tansgenic plantlets expressing the introduced gene. Leaf sections were more sensitive than stem sections to kanamycin and thought to be better material for transformant screening. The bacterial density did not affect on the efficiency of transformation over the range of 4×10^5∼7×10^9 cfu. The optimum period for co-cultivation was one day or shorter. Both of the optimum concentrations of cefotaxime and ampicillin in the medium were 250 ㎍/㎖ for elimination of bacteria from the inoculated leaf sections. The addition of acetosyringone in the bacterial culture medium increased transformation rate, and the highest rate was obtained at 50 μM of acetosyringone. The transformed galls could be selectively induced and gown on the growth regulator-free medium or on the medium containing 100 ㎍/㎖ or higher contrition of kanamycin. The roots were induced from the galls incited by A rhizogenes within 3 weeks on the growth regulator-free medium as well as on the medium containing growth regulators. The plantlets were regenerated from the galls cultured for 6 weeks on the medium containing 0.05 ㎎/㎖ of NAA and 0.5 ㎎/㎖ of BA. The expressions of the introduced opine gene in the transformed galls and plantlets were confirmed by the analysis of agropine and mannopine.