Immmune parameters of the Manila clam Ruditapes philippinarum collected from four tidal flats, Nudong, Gonam, Hwangdo and Bangpo on Anmyeon-do, Korea were optimized and evaluated at the single cell level using flow-cytometry Hemocytes were withdrawn from the sinus of each clam, and total hemocyte counts (THC), phagocytosis rate, hemocyte mortality (HM) and DNA damage of hemocyte were analyzed. The highest hemocyte counts was recorded from the clams collected from Gonam, followed by Hwangdo, Nudong and Bangpo (P<0.001). Phagocytosis rate and hemocyte mortality of Gonam and Nudong clams were significantly higher than those of clams from Hwangdo and Bangpo (P<0.001). DNA damage in the clams from Nudong was higher twice than that of clams from Gonam (P<0.05). We suggest that the flow-cytometry has a high potential for evaluation of immunity of marine bivalves.