W ith the comp letion of the Populus genome sequence in 2006, the study on functional genomics in Populus has become a major task. Establishment of Populusmutant population is an essential app roach for forestry functional genomics study. The activation tagging is a p romising and powerful method to constructmutant library of Populus and to further discover new gene and elucidate its function now. A novel T-DNA activation tagging pCAS05was constructed for forest functional genomics in this study. We could select conveniently and easily transgenicp lants by sp raying Basta because bar gene is constructed in this vector as a selection marker. Moreover, we couldalso construct a large scale mutant library in Populus by this activation tagging because of effectively selection of bargene.