The objective of this study is to study the seasonal variations of the post-natal development of the testis of Ouled Djellel lambs born in semi-arid zones. The study was conducted on lambs born in October at the pilot farm Bouali Hamdene, located 15 km from Sigus, wilaya Oum El Bouaghi. The testes with the epididymis were dissected from the genitalia of rams born in October at the age of 0 (<24 hours), 4, 12, 20, and 32 weeks. The testes with the epididymis were weighed, measured, and placed in the aqueous Bouin fixative and prepared for histological study. The histological development of different testicular structures during the postnatal period was elucidated. Testicular growth between 0 and 32 weeks of age was associated with remarkable changes in testicular histology including increased tubular tissue volume, tubular diameter and length, and spermatozoa. It has been deduced that these lambs have reached puberty between the ages of 5 and 6 months (between March and April) and that the season and the change in temperature may have an effect on the age of puberty. It is concluded that the histological development of the testis, especially the seminiferous tubules of the Ouled Djellel lambs during the postnatal period, is necessary to acquire reproductive capacities to reach the age of sexual maturity. This age is influenced by several seasonal and physiological factors.