Despite abundant germplasm resources in Southwest China for poplar genetic improvement,the varied species exist tiny difference in morphology and have unknown systematic relationship.Using Populus davidiana as outgroup,the phylogenetic relationship of 36 specimens covering 17 species or hybrids collected from Southwest China and other areas was explored based on sequence data of chloroplast atpF-atpH,trnL-F,matK and nuclear ITS.The results showed that:(1)the ranges of length in atpF-atpH,trnL-F and matK were 605-634 bp,957-1 010 bp and 819 bp respectively,and the combination of 3 chloroplast fragments had 29 variable sites and 15 informative sites,while the aligned length of ITS fragment including 19 variable sites and 17 informative sites was 646 bp.(2)The average genetic distance among all samples of chloroplast combination was 0.001 3 and that of ITS fragment was 0.003 6.Based on chloroplast combination data,the result of MP tree was consistent with that of Bayesian algorithms and both suggested the Populus section Tacamahaca species were divided into 2 clades,of which,clade 1 was formed by P.cathayana,P.trinervis,P.ussuriensis,P.maximowiczii,and the species in clade 2,namely,P.simonii,P.pseudo-simonii,P.szechuanica,P.haoana,P.qamdoensis,P.xiangchengensis,P.kangdingensis,P.schneideri,P.yunnanensis,P.szechuanica var.tibetica,could not be clearly separated and had close relationship with P.ciliata.(3)Although a few differences in phylogenetic tree based on chloroplast combination data,ITS fragment provided that P.pseudo-simonii existed closer affinity with other species in clade 1 (e.g.P.simonii and P.szechuanica) but larger genetic distance with others in clade 2.The results of this study made a understand on the phylogeny of poplar in section Tacamahaca species from Southwest China,and provided a scientific bases for their systematic classification and evolutionary relationship.