Objective:To study the expression of receptor accessory protein 6(REEP6) in the testis and sperm of adult male humans,and approach the potential function of the protein in the male reproductive system. Methods:The expression of REEP6 in human testis and sperm was confirmed by Western blot. Immunohistochemical staining was used for detecting REEP6 localization in testis tissue,and immunofluorescent staining was used for detecting REEP6 localization in both testis and sperm before and after the acrosome reaction. Results:REEP6 was presented in both human testis and sperm. In the testis,REEP6 immunoreactive particles were observed mainly in the membrane of different stages of spermatogenic cells. In human sperm,its immunoreactivity was restrictively localized to the posterior head where sperm-egg fusion took place,and the REEP6 localization was not affected by sperm acrosome reaction. Conclusion:Expression of REEP6 in the male reproductive system of the adult human exhibits cell-and region-specific patterns,which suggests that they may play an important role in spermatogenesis and/or sperm-egg fusion.