Abstract: Lignin is an important component of wood, mainly for mechanical support, water transport and defense against pests and diseases. The 4CL enzyme is one of the key enzymes in controlling the pathway of lignin synthesis. The Pag4CL3/4CL5 gene was cloned from 84K poplar leaf cDNA by PCR. GenBank accession numbers are MK183033(Pag4CL3) and MK183034(Pag4CL5). The functions and characteristics of the two genes were analyzed using bioinformatics software. The similarity of the 4CL3/4CL5 proteins in 84K poplar and the 4CL3/4CL5 proteins in Populus trichocarpa were 97%,and they contained two conserved motifs of SSGTTGLPKGV and GEICIRG; subcellular localization showed the main localization of Pag4CL3/4CL5 proteins. In the endoplasmic reticulum, it may be a membrane protein and both are hydrophilic proteins. The expression of the Pag4CL3/4CL5 gene in different tissues was analyzed by qRT-PCR. The results showed that the Pag4CL3 gene was mainly expressed in leave and stem, and the expression level in root and top buds was low. The Pag4CL5 gene showed high expression level in leave and root, and low level in stem and apical buds. Pag4CL3 and Pag4CL5 may function together in the leaves, however, Pag4CL5 ismainly function in the root, and Pag4CL3 mainly function in the stems.