Abstract: Using phase contrast microscopy and electronic transmission microscopy,five types of hemocytes were determined in the larvae of Ostrinia furnaclis,namely granularcytes,plasmatocytes,oenocytoids,prohemocytes and spherule cells.Total hemocyte counts (THC) and differential hemocyte counts (DHC) were compared in the larval hemolymph.From the late stage of 3rd instar till the 5th day of 5th instar,THC increased shortly before and after ecdysis and thereafter decreased to a basal level.During the 1st day to the 5th day of 5th instar,the amount of plasmatocytes increased before the 3rd day and decreased after that,but granularcytes were the reverse.In in vitro test both plastomatocytes and granularcytes showed spreading and adhesive behavior but their spreading ability were different.When Sephadex A-25 beads were injected into the 5th-instar larvae they were soon encapsulated and some of them were melanized.Hemocytes were also able to encapsulate the latex beads in in vitro test.No difference of the capsule structure could be seen.