Objective:To investigate the expression and possible function of RhoA in human male reproduction. Methods:RT-PCR was used to detect RhoA mRNA, Western blot and Immunohistochemistry were used to detect the RhoA protein expression in human testis,epididymis and mature spermatozoa. The localization of this protein on human spermatozoa was determined by indirect immunofluorescent staining using anti-RhoA antibody. The percentage of acrosome reaction was determined by PSA staining. Results:RhoA mRNA was only detected in the epididymis,but its protein could be expressed in mature sperm as well as in the epididymal epithelium. RhoA was localized on human sperm entire acrosome and the flagellum,and it was translocated to the equatorial regions and post-acrosomal region after acrosome reacted. Meanwhile,the percentage of acrosome reacted sperm was decreased in comparison to pre-immune control after treatment with specific anti-RhoA antibody(P < 0.01). Conclusion:The results suggest that RhoA might be absorbed or incorporated into the human sperm plasma membrane during epididymal transition and could help human sperm to develop the ability to undergo acrosome reaction.