摘要Objective. To study expression and localization of Smad4 protein, the common-mediator Smad, which is one of intracellular signaling molecules of transforming growth factor-β (TGF-β) family, in rat testis during postnatal development. Methods. In this study, whole testes were collected from S.D rats aged 3 days, 7 days, 14 days and 28 days, and adult respectively. We examined the cellular localization and developmental change of Smad4 in rat testis by immunohistochemical ABC method with glucose oxidase-DAB-nickel enhancement technique; the quantitative analysis of the immunostaining by the image analysis system; the Smads pro-teins coexistence in the adult rat testis by the double immune staining for CD14 - Smad4 and Smad2 -Smad4; the protein expression of Smad during rat testicular development by means of Western blots. Results. The protein of Smad4 was present in rats from 3 days of age to adulthood, and the immunolocalization was exclusively localized to the cytoplasm of Leydig cells with negative nuclei in the in terstitial tissue at any time point. No expression was detected in germ cells. The result of image and statistical analysis showed that generally, there was a tendency that the expression of Smad4 in the testes increased gradually with the rats developing maturation. Conclusion. Our data provide direct evidence for the molecular mechanism of TGF-β action in rat testes during postnatal development and spermatogenesis of rats.