Abstract: To understand the genetic and molecular mechanisms during floral development in Populus tomentosa, we isolated a full-length cDNA sequence of PtlabA-like1 gene from female floral bud cDNA library of P. tomentosa, with the method of bacteriophage absorption by filter paper-PCR. A conserved LabA-like superfamily domain was found via searching Conserved Domains Database. Therefore, it was given by the name PtlabA-like1. A phylogenetic tree was constructed using BioEdit and MEGA3.1 softwares to depict its evolutionary relationship with other 9 members comprising the same domain that retrieved via BLAST at JGI. The expression patterns of LabA-like superfamily members in tissues of P. tomentosa were estimated by RT-PCR. Results revealed that PtlabA-like1 and PtlabA-like6 had similar expression domains at stems, young leaves, mature leaves, male and female flower buds, but a higher abundance was especially shown in PtlabA-like1. PtlabA-like8 was detected with a low level at root only. Other members which had different abundances had a constitutive expression pattern at all of the six tissues. Furthermore, constitutive expression vector carrying 35S::PtlabA-like1 was constructed. All of these would provide the groundwork for understanding the function of PtlabA-like1 gene.