Background: The testis is the primary reproductive organ in the male, it is an ovoid organ covered from outside inwards by, the tunica vaginalis, tunica albuginea and tunica vasculosa. Each testis is separated from its fellow by a fibrous median raphe, which is deficient superiorly. The testis consists of numerous lobules, about 250-400, each lobule contains from one to three, or more convoluted tubules. Objectives: The aim of this work was to study the prenatal and postnatal development of the albino rat testes considering its structure and maturation. Methods: 35 healthy, non-pregnant female and 18 male albino rats weighing (200-250 g) were obtained from the animal house, Faculty of Medicine, Zagazig University. After mating and pregnancy, the rat embryos and offsprings were divided into 3 groups and 9 subgroups; Group A (13th, 16th &18th day fetal rats), Group B (1st, 10th, 15th &21st postnatal days rats) and Group C (2 months and 6 months old rats). The fetal rats (13th and 16th) were fixed as whole, while the remaining prenatal, postnatal and adult rats were dissected to obtain testes, which were processed for light and electron microscopic examinations, morphometric and immunohistochemical studies. Results: Albino rats at prenatal day 13 (E13) showed the gonads were formed of genital ridges which were present on the posterior abdominal wall on both sides of the developing dorsal aorta. Albino rats at prenatal day 16 (E16) showed The sex cords were transformed into fetal seminiferous cords in the form of compact structures without lumen. The testes at prenatal day 18(E 18) showed the seminiferous cords form the main bulk of the testis and the interstitial tissue nearly completely differentiated with small amount of connective tissue in the spaces between seminiferous cords especially in the center. In postnatal day 1,10,15(D1,D10&D15) showed The parenchyma of testis was consisted of multiple rounded and elongated seminiferous cords. In postnatal day 21 (D21), The parenchyma of testis was consisted of multiple closely packed ovoid shaped seminiferous tubules, some of them still cords with no lumina. In adult group, The parenchyma of testis consisted of large multiple seminiferous tubules, separated by relatively narrow interstitial spaces and attained lumina containing sperms. Immunohistochemistry showed positive reaction to proliferative cell nuclear antigen (PCNA) at E13, E16 & E18. Also positive reaction to (PCNA) showed in postnatal and adult groups. Conclusion: Sexual differentiation of the gonads in albino rats starts after 13 days of gestation and the development of testes in albino rats is completed postnatally reaching full maturation at about age of two months.