The SOX2 protein is an important transcription factor functioning during the early development of animals. In this study, we isolated a full-length c DNA sequence of scallop Chlamys farreri sox2, Cf-sox2 which was 2194 bp in length with a 981 bp open reading frame encoding 327 amino acids. With real-time PCR analysis, it was detected that Cf-sox2 was expressed in unfertilized oocytes, fertilized eggs and all the tested embryos and larvae. The expression level increased significantly(P < 0.01) in embryos from 2-cell to blastula, and then decreased significantly(P < 0.01) and reached the minimum in umbo larva. Moreover, location of the Cfsox2 expression was revealed using whole mount in situ hybridization technique. Positive hybridization signal could be detected in the central region of unfertilized oocytes and fertilized eggs, and then strong signals dispersed throughout the embryos from 2-cell to gastrula. During larval development, the signals were concentrated and strong signals were restricted to 4 regions of viscera mass in veliger larva. In umbo larva, weak signals could be detected in regions where presumptive visceral and pedal ganglia may be formed. The expression pattern of Cf-sox2 during embryogenesis was similar to that of mammal sox2, which implied that Cf-SOX2 may participate in the regulation of early development of C. farreri. The SOX2 protein is an important transcription factor functioning during the early development of animals. In this study, we isolated a full-length c DNA sequence of scallop Chlamys farreri sox2, Cf-sox2 which was 2194 bp in length with a 981 bp open reading frame encoding 327 amino acids. With real-time PCR analysis, it was detected that Cf-sox2 was expressed in unfertilized oocytes, fertilized eggs and all the tested embryos and larvae. The expression level increased significantly (P <0.01) -cell to blastula, and then decreased significantly (P <0.01) and reached the minimum in umbo larva. Moreover, location of the Cfsox2 expression was revealed using whole mount in situ hybridization technique. Positive hybridization signal could be detected in the central region of unfertilized oocytes and fertilized eggs, and then strong strong signals distributed throughout the embryos from 2-cell to gastrula. During larval development, the signals were concentrated and strong signals wer e restricted to 4 regions of viscera mass in veliger larva. In umbo larva, weak signals could be detected in regions where presumptive visceral and pedal ganglia may be formed. The expression pattern of Cf-sox2 during embryogenesis was similar to that of mammal sox2, which implied that Cf-SOX2 may participate in the regulation of early development of C. farreri.