To investigate the differences in expression of xyloglucan endotransglycosylase gene(PbXET) in ‘Dangshansuli’ and its russet mutant ‘Xiusu’ pear(Pyrus bretschneideri Rehd.),we cloned the cDNA fragment of PbXET by rapid amplification of cDNA ends(RACE).The level of relative expression of PbXET in leaf,exocarp and sarcocarp and in the exocarp at different stages(days after full bloom,DAFB) were determined by real time quantitative reverse transcription-PCR(qRT-PCR).The results showed that:(1)PbXET3,with the accession number of KJ690921 in the National Center for Biotechnology Information(NCBI),and PbXET4,with the accession number of KJ690922 in NCBI had a open read frame(ORF) of 903 bp and 891 bp,respectively,encoding the corresponding polypeptide of 300 amino acids or 296 amino acids.Clustering analysis by sequences of amino acids showed that the structure of PbXET3 and PbXET4 in pear plant had a closer relationship to MdXET-3 and MdXET-5 in apple plant respectively.(2)The results of semi-quantitative PCR demonstrated that PbXET3 and PbXET4 had expressed in leaf,exocarp and sarcocarp of ‘Dangshansuli’ and its russet mutant ‘Xiusu’ pear at 150 DAFB,but expression of the two genes were lower in leaves and higher in exocarps and sarcocarps.Compared with PbXET4,the relative levels of PbXET3 expression were lower in leaves,but were higher in exocarps and sarcocarps.(3)The expression of PbXET3 and PbXET4 genes showed different trend lines of the dynamic change in exocarps of ‘Dangshansuli’ and its russet fruit mutant ‘Xiusu’ pear.The expression of PbXET3 decreased sharply after the beginning of exocarp turning russet(100 DAFB),whereas,the expression of PbXET4 decreased before 100 DAFB in exocarps of ‘Xiusu’ pear in compare with that of ‘Dangshansuli’ pear.It was postulated that the expression of PbXET3 and PbXET4 may be involved in formation of russet exocarps in pear fruit,and the difference in the expression of the two genes could be one of the important reason why the structure of exocarps cells in ‘Xiusu’ pear altered.