This study has been carried out to morphologically investigate in vitro immune reactions of both normal hemocytes and in-vivo-E. coli-exposed hemocytes of Artogeia rapae to Escherichia coli. Most of the normal hemocytes, which were gathered into various sizes of groups, did not show phagocytotic activities to E. coli, while a part of them, which were in free-cell state, actively phagocytosed. The hemocytes, which were exposed in vivo to E. coli, were degraded to numerous vesicles. These E. colis supposed to react with degrading hemoctes were attached to many small electron-dense particles. Some of E. coli had structural damages in their cell wall.