Introduction: Thai red jungle fowl (Gallus gallus gallus) has been focusing on genetic profiles besides phenotypical features. The husbandry of this species is still limited. Basic understanding of its reproductive systems may be useful for breeding applications. Additionally, the morphology of testes and epididymis of Thai red jungle fowl has never been elucidated. Material and Methods: This study has examined the gross structure and histology of those organs of male Thai Gallus gallus gallus at 24th weeks (age and sexual maturity). Moreover, the localization of sterodogenic acute regulartory (StAR) protein in the testis was also performed by immunohistochemistry. Results: The results showed that the mature testes were oval shape with 1.56 ± 0.584 cm. in length and 1.20 ± 0.067 cm. in width, respectively. General histology of testes and epididymis was similar to those of maturely domestical birds. Expectedly, the StAR protein was first localized in the leydig cells of Thai red jungle fowl. Conclusion: These findings are fundamental data that may be applied to the breeding process.