Abstract: As an important component of plant cell wall, expansins widely present in plant genome and have unique loosening冶effects and are thought to function in plant growth, development, plant resistance, etc. Whole genome sequencing of poplar reveals it containing 36 expansin genes classified in to 4 subfamilies (EXPA, EXPB, EXLA and EXLB). Systematic bioinformatics analysis showed that poplar expansin genes had the conserved apparent sequence features and stable protein structure. It obviously displayed 9 different introns originate modes and 6 high-frequency codons. Transcriptome analysis showed that the expansin genes expressed highly in poplar wood forming tissues or organs, and were associated with the reproductive development. The results here displayed the basic information of poplar expansin superfamily which could be a good platform for the gene function study in future.