Abstract: Bellamya purificata as a unique edible freshwater snails in China has very considerable economic value. To study the role of the steroidogenic enzyme gene Cyp17a1 in the hormone synthesis process of B.purificata, this study cloned the open reading frame (ORF) region of the Cyp17a1 gene. The expression patterns of Cyp17a1 in B.purificata were analyzed using quantitative real-time PCR and in situ hybridization. RNA interference was performed on the Cyp17a1 gene, and B.purificata were immersed in different concentrations of hormones to explore the role of Cyp17a1 in the synthesis of steroid hormones. The results showed that the ORF region of Cyp17a1 in B.purificata is 1 572 bp in length, encoding 523 amino acids. The expression of Cyp17a1 varied across different tissues of B.purificata, with significantly higher expression in males than in females, except in the gills. The gene was primarily expressed in spermatocytes and spermatids in the testes. After 12 hours of RNA interference with Cyp17a1 in the gonads, testosterone levels significantly decreased in both males and females, while estradiol levels significantly increased. Immersion in different concentrations of hormones for 24 days revealed that treatment with 40 ng/L of 17β-estradiol (E2) and 17α-methyltestosterone (MT) resulted in an initial decrease followed by an increase in Cyp17a1 expression. In contrast, treatment with 200 ng/L of E2 and MT led to an initial increase followed by a decrease in Cyp17a1 expression. These findings indicate that Cyp17a1 is involved in the synthesis and transformation of steroid hormones in B.purificata. This study provides valuable insights into the steroid hormone synthesis process in B.purificata and lays a theoretical foundation for research on sex regulation and gonadal development in this species.