To understand the role of hemocytes in the shell repair process, a hole was drilled in the right valves of the Pacific oyster, Crassostrea gigas, and the repair process was observed. Histological observations suggested that the exterior surface of the shell was repaired by aggregated hemocytes. The nuclei of the hemocytes were cleary stained in the regenerated shell while appearing fragmented after calcification at the $7^{th}$ day. Globular calcium granules were genegenerated from the hemocytic monolyer after 6 days of incubation which were morphologically and chemically identical with those from prismatic shell. Our finding suggested that the repaired prismatic shell was composed by aggregated hemocytes and that their endogenous calcium component might support the nucleation of calcium biomineralization during shell repair.