In this study,a Phi class GST named PtoGSTF4 was cloned from Populus tomentosa.PtoGSTF4 encodes a protein of 213 amino acid residues.RT-PCR revealed that PtoGSTF4 was a constitutively expressed gene that is expressed in stem,leaf and phloem of stem of P.tomentosa under normal growth condition,and H₂O₂ and atrazine stressed conditions.The recombinant PtoGSTF4 was expressed in E.coli and purified by Ni²⁺ sepharose affinity chromatography.PtoGSTF4 showed enzymatic activities towards substrates CDNB,NBD-Cl,NBC and Cum-OOH.Kinetic analysis found that the affinity of PtoGSTF4 to GSH was higher than that to CDNB.PtoGSTF4 had optimal pH ranging from 7.5~10.5 and optimal temperature ranging from 30 ℃~60 ℃.Our results indicated that PtoGSTF4 may play important roles in stress tolerance in P.tomentosa.