Abstract: Choline oxidase gene (codA) was introduced into the haploid plants of Populus simonii × P. nigra by Agrobacteri ummediated approach, with axenic leaves used as explants. PCR and Southern blot analysis confirmed four kanamyc in-resistant transgenic plants, in which codA successfully integrated into the genome of Populus simonii × P. nigra haploid plants. Real-time quantitative PCR revealed that the transgene was expressed in the transgenic plants at different levels. Salt tolerance test demonstrated that the 4 transgenic plants could grow normally at 0.6% salinity, but nontransgenic plants suffered severely from the same salinity. Thus, the expression of codA gene improves the salt-stress tolerance of these transgenic poplar plants.