Due to the importance of sea cucumbers and the paucity of information about the status of Iranian populations, this study was necessary. Therefore, the biology of the reproduction system and macroscopic and microscopic examinations of the sexual glands of Holothuria leucospilota were carried out in this study. Data were obtained from monthly sampling of H. leucospilota during a one-year period on the Bustaneh Coast of the Persian gulf, Hormozgan, Iran. A total of 124 females and 108 males were collected. The gonads were found to be composed of many tubules. The gonad color of males of this species is creamy, while female gonads are pink to reddish-orange. Macroscopic and microscopic features of the gonads were used to assess maturity stages. The studied macroscopic features were gonad color, gonad weight, their length and diameter, and the number of tubules. Microscopic examinations included histological studies of hemotoxylin and eosin (H&E) stained texture slides. Based on these criteria, five stages of maturity were determined for both sexes: early growth (1), growth (2), advanced growth (3), mature (4), and post spawning (5). The tubules were found to be longer and narrower in males than in females. The measured biometric factors of gonadal tubules developed from stage 1 to stage 4 of sexual maturity and declined in stage 5. The relationship between the number of tubules and the gonad weight was also calculated. The coefficient of a diagram was determined as 0.73 for male and 0.80 for female H. leucospilota.