The razor clam Sinonovacula constricta is an economically important cultured mollusk in China, but the molecular mechanism of its gonadal development and sexual differentiation remains unclear. In this study, proteomic analysis of gonadal tissues was performed to identify key sex‑biased proteins. A total of 3,217 differentially expressed proteins (DEPs) were detected between testes and ovaries. Among these, members of the Tektin family, Ropporin‑1, and Tssk proteins were significantly upregulated in the testis, whereas Histone H1 and FAT4 showed elevated expression in the ovary. These sex‑specific protein signatures suggest that structural components of flagellar motility (Tektins, Ropporin‑1) and spermatogenesis‑related kinases (Tssk) are preferentially enriched in the male gonad, while chromatin‑associated proteins (Histone H1) and atypical cadherins (FAT4) are more prominent in the ovary. Our proteomic dataset provides a comprehensive protein‑level resource for understanding gonadal development and sexual differentiation in S. constricta, and highlights candidate protein markers for future reproductive and breeding studies.