Introduction: Understanding the dynamics of spermatogenesis is crucial to clinical andrology and to understanding the processes which define the ability to produce sperm. However, the entire process cannot be modeled in vitro and guinea pig may be an alternative as animal model for studying human reproduction. Objective: In order to establish morphological patterns of the testicular development and spermatogenesis in guinea pigs, we examined testis to assess changes in the testis architecture, transition time from spermatocytes to elongated spermatids and stablishment of puberty. Materials and methods: We used macroscopic analysis, microstructural analysis and absolute measures of seminiferous tubules by light microscopy in fifty-five guinea pigs from one to eleven weeks of age. Results: Differences in relation to mass, length and width of the testes appeared at week 3 and were intensified in week 6 with the puberty. At week 2 the first spermatocytes at preleptotene/leptotene appeared, indicating the onset of meiosis. At week 6 the seminiferous tubules formed lumen, differentiated Sertoli cells and all kinds of germ cells; spermatozoa released into the lumen and the largest expansion of tubular diameter and height of the seminiferous epithelium occurred. Transition time from spermatocytes to elongated spermatids was estimated in 21 days. Conclusion: We conclude that the testicular development and puberty are faster than in other mammal and rodent species, demonstrating the suitability of the guinea pig testes as a model for studies of the testicular development and spermatogenesis.