Abstract: Based on transcriptome study of cucumber fruit set，a β-expansin gene：CsEXPb1 was cloned and investigated in present study. Homolog BLAST showed that CsEXPb1 is belonged to Calmodulin-like Protein family，and has high similarities with the expansin genes of Cucumis melo，Fragaria vesca subsp. vesca and Solanum lycopersicum. The ExPasy analysis showed that CsEXPb1 is a hydrophilic protein；The subcellular localization analysis indicated that CsEXPb1 localized in plasma membrane，cytoplasm and nucleus；qRT-PCR analysis found that CsEXPb1 was up-regulate expressed during pollination and parthenocarpy fruit set in cucumber，while down-regulated during fruit abortion；qRT-PCR also showed that the transcription of CsEXPb1 could be cis-regulated by fruit-set inducing hormones i.e. auxin，cytokinin and gibberellin. Therefore，it was speculated that CsEXPb1 may be close related to hormone induced parthenocarpic fruit set of cucumber.

Key words: cucumber, expansin, CsEXPb1 gene, expression analysis, fruit set, parthenocarpy