Hemicelluloses are one of the major components in plant cell walls. It is believed that glycosyltransferases are responsible for the biosynthesis of polysaccharides, including cellulose and hemicelluloses. To date, only a few glycosyltransferase genes related to hemicelluloses biosynthesis have been identified and these genes were characterized from non-woody plants. Since secondary cell walls in wood are the major resource of renewable biomass, it is essential to investigate hemicelluloses biosynthesis in secondary cell walls in woody tissues. The objective of this study is to identify glycosyltransferases genes involved in hemicellulose biosynthesis in secondary cell walls of wood. Xylan is a predominant hemicellulose in hardwoods, of which xylose is the principle sugar unit. To investigate xylosyltransferase genes involved in hardwood xylan biosynthesis, we used Arabidopsis alpha-1, 6-xylosyltransferase cDNA as a probe to screen a P. tremuloides Michx. developing xylem cDNA library. Two putative glycosyltransferase genes were isolated and fully sequenced, designed as PtGT1 and PtGT2. Alignment results showed that PtGT1 and PtGT2 share a high degree of identity and similarity with Arabidopsis alpha-1, 6-xylosyltransferase at amino acid level. In order to identify the putative xylosyltransferase genes in a model forest tree, P. trichocarpa, PtGT2 cDNA was labeled and used as a probe to screen a P. trichocarpa developing xylem cDNA library. Two putative glycosyltransferase genes were identified as well, named as PtriGT1 and PtriGT2. Sequence analysis demonstrated that PtriGT1 and PtriGT2 are nearly identical to PtGT1 and PtGT2, respectively. Molecular characterizations were conducted for PtGT1/PtriGT1 and PtGT2/PtriGT2. The expression data of Northern blot and in situ hybridization indicated they are specifically and strongly expressed in developing xylem. Moreover, antisense technology and siRNA-mediated RNA interference have been applied to down regulate the expression of these genes in transgenic plants. Further characterization of transgenic plants will provide us important evidences about the biological functions these genes are conferring.