Abstract: Crassostrea angulata is a major commercial species for the shellfish aquaculture in southern China. To investigate the reproductive endocrinology of mollusc, we studied the gene of enzymes involved in steroid metabolism in C. angulata with molecular biology technology. We obtained the fulllength cDNA 17β-HSD (1 149 bp) encoded peptides of 307 amino acids. 17β-HSD mRNA transcripts were expressed in most tissues of oyster with the highest level in gonad (p<0.05). The expression of 17β-HSD was lower during the gonad maturation of C. angulata, but higher in the initiation and partially spent stages (p<0.05). Furthermore, results obtained in situ hybridization indicated that 17β-HSD mRNA signals were detected in the follicle cell of ovary. Together with the in situ hybridization and qRT PCR results, it is suggested that 17β-HSD may play an important role in the regulation of gonad development based on steroidogenesis mechanism in C. angulata.