Reproduction in wild animals is not well studied, which explains the limited information available on the male reproductive system of the brown rat (Rattus norvegicus). This work presents a histomorphometric comparison between the male reproductive system of the brown rat, which is poorly investigated, and the white Wistar rat, which is well-explored as a laboratory strain. Cross-sectional and longitudinal sections were made of the testes, epididymis, vas deferens, and seminal vesicles, and these sections underwent various histomorphometric analyses. The results indicate a structural similarity between the two species in the epididymis and the testes, which exhibit large seminiferous tubules. However, morphometric analysis reveals differences in the surface area of the seminiferous tubules between the two species, as well as variations in epithelial cell height, nuclear height, and supranuclear space height in the epididymis. For the vas deferens and seminal vesicle, the histological results of both species are almost identical; however, morphometric data indicate notable differences