Electron microscopical studies were performed on gametogenesis and fertilization of the gametes developed in the prolonged culture of P. falciparum. gametocytes which appeared during the culture of the parasites in the gametocytogenesis-induction medium. When the erythrocyte plasma membrane separated from the gametocyte during gametogenesis, a small part of the gametocyte cytoplasm which was enveloped with the multilayered sheaths of the erythrocyte plasma membrane, was released from the gametocyte into culture medium. We could observe the process of penetration of the macrogamete cytoplasm by the microgamete and then the fusion of the membrane surrounding microgamete with the nuclear envelope of macrogamete. From the findings of two microgamete nuclei were present in the cytoplasm of a macrogamete at fertilization, it is assumed that the multiple nuclear-fusion may occur.