Abstract: In order to provide basic data for the full artificial reproduction of Siganus oramin, we used the biological anatomy and tissue sections to study the first sexual maturation of gonadal development of S. oramin cultured in pond. From January to July 2019, we obtained the histological sections of gonads of S. oramin of 1⁺ year-old, and calculated their gonado somatic index (GSI) and hepato somatic index (HSI). The results show that the development of gonads could be divided into five stages (Stage II, III, IV, V, VI). Gonad at Stage I was not found. All of the gonads were at Stage II in January. The ovary was still at Stage II in February, but part of the testis developed to Stage III. About half of the ovaries developed to Stage III in March. A few individuals developed to Stage IV. The testis was mainly at Stage IV, and partly developed to Stage V, and sperm could be squeezed out. The GSI was maximum in April, and the testis basically developed to Stage V. A small part of the ovary matured, and most of them stayed at Stage III and IV, with a small amount still at Stage II. In May, the gonads briefly entered Stage VI after reproduction, and then rapidly degenerated. Immature gonads stopped developing and began to degenerate. The gonads degenerated to Stage II in June and remained in July, and the GSI decreased further. The GSI of the first sexual maturity of female S. oramin cultured in pond was 1.74‰−133.44‰, and that for the males was 1.06‰−138.5‰, both showing a peak in March−May. The variation trend of HSI and GSI was consistent, but HSI peaked about a month in advance. The ovarian development of S. oramin is completely synchronous, and the fish spawn once a year with a breeding period from the end of March to the beginning of May.