More concerns have been focused on transgenic trees than transgenic food crops because of their longevity and the likelihood that transgene might spread to related species of wild trees grown nearby. Detailed, the long life span of trees could increase the likelihood of transgene instability, affect diversity of non-target organisms, improve resistance to insecticidal proteins, increase invasiveness of the tree itself (weediness), and arouse negative environmental consequences or new environmental risks resulted from gene flow or gene escape. The transgenic black poplar Populus nigra carrying Bt gene and hybrid white poplar clone 741 Populus alba x (P. davidiana+P. simonii) x P. tomentosa carrying fusion genes, which are resistant to leaf insects, have been commercial release in China since 2002. In this review, we provide a brief overview of biosafety assessment researches on transgenic insect-resistant poplar varieties during the last decades. Arthropod population and community structure have changed within the transgenic poplar plantations, and the diversity of the insect community has increased. But there are no significant changes for soil microbial communities. Gene flow monitoring in the transgenic black poplar plantation showed that the probability of gene escape is very low via pollen and seeds. The potential environment risk was also evaluated based on the experiments of horizontal gene transfer from transgenic poplars through endophytic bacteria. We pointed out the necessity of the biosafety assessments concerning the transgenic poplars when intercropping with food crops.