Dmrt5, an important member of the Dmrt gene family, is a transcription factor closely related to sex determination, gonad development and organ function maintenance in animals. In order to investigate the roles of Dmrt5 genes (ScDmrt5) in gonadal development of Sinonovacula constricta, the full-length cDNA sequences of the two ScDmrt5 were cloned and identified, and the expression patterns of ScDmrt5 genes/proteins during gonadal development were investigated. Based on sequence comparison and phylogenetic analysis, the two genes were named ScDmrt5-1 and ScDmrt5-2, encoding 389 and 374 amino acids, respectively, both of which possessed DM and DMA conserved structural domains. In the gonadal mature stage, ScDmrt5-1 and ScDmrt5-2 were all expressed in seven tissues, and the expression level in the testis was significantly higher than that in the ovary (P＜0.05). During gonadal development, the expression level of ScDmrt5-1 gradually increased with the development of the testis, and the expression level was highest in the mature stage (P＜0.05), while the expression trend was opposite in the ovary. The expression level of ScDmrt5-2 gradually increased with the development of testis, but the expression level was all lower and without significant difference among different developmental stages of ovary. The immunofluorescence results showed that ScDmrt5-1 and ScDmrt5-2 proteins were mainly located in the germ cells of male and female gonads during gonadal development, such as spermatogonia, spermatocytes and mature sperm of testis, and oocytes, oocytes and mature oocytes of ovary. In conclusion, ScDmrt5-1 and ScDmrt5-2 may be mainly involved in the development and functional maintenance of testis, and may be also involved in respiration, neuroperception and so on.