Abstract: To better understand the molecular mechanisms underlying germ cell development in stony corals, this study focused on proliferating cell nuclear antigen (PCNA), which is an auxiliary protein of DNA polymerases and is principally responsible for DNA replication and repair. We performed the molecular identification and characterization of the complementary DNA for the pcna gene in the stony coral Euphyllia ancora. Quantitative reverse transcription-polymerase chain reaction analysis and Western blotting with anti-E. ancora PCNA antibody demonstrated that E. ancora PCNA gene products (transcripts and proteins) were present in all polyp tissues, including the testis and ovaries. Immunohistochemical analysis of spermatogenesis showed that intensive immunoreactivity of PCNA (irPCNA) was detected in the nuclei of spermatogonia. The irPCNA was also weakly detected in spermatocytes, and became almost undetectable in the spermatids and sperm. In contrast, in female germline cells, the irPCNA was detected in the nuclei of oogonia and all stage of oocytes. These results suggest that PCNA plays an important role in both the mitotic and meiotic processes of the coral germ cells. To the best of our knowledge, this study is the first to show the expression profile of the PCNA protein and its subcellular localization in coral germ-cell development.