Abstract: A complete fragment representing the PtrWRKY25 (Potri.007G078200.1), was isolated from Populus trichocarpa. by reverse transcription PCR(RT-PCR). Displaying significant similarity with other WRKY factors in Arabidopsis’s AtWRKY12, Vitis vinifera’s VvWRKY2 and Medicago truncatula’s MtSTP gene. The expression profiles of PtrWRKY25 showed the highest transcript level in stem and relatively low level in phloem and xylem. Plant tissue sections between phloroglucinol staining found PtrWRKY25 transgenic lines compared with wild-type secondary wall is also a decreasing trend. To investigate the in vivo function, PtrWRKY25 was expressed under control of the CaMV35S promoter in Populus trichocarpa. by Agrobacterium-mediated transformation. About 1 time lower accumulation of lignin was detedted in transgenic plants harboring PtrWRKY25, coincide with the toluidine blue staining of stem. Our findings suggested that PtrWRKY25 might play more important roles in biosynthesis of lignin.