Ultrastructure of the hemocytes during metamorphosis in Lymantria dispar L. was studied using transmission and scanning electron microscopes. In prohemocyte, nucleus became irregular shaped, which keterochromatin was more rich and electron density of its cytoplasm decreased during metamorphosis. In plasmatocyte, elongated mitochondria, electron dense small granules, and micropapillae were decreased in number in pupal stage. Plasmatocyte in the larval and pupal stage phagocytosed the foreign material. The number of the granulocytes and the granules within it increased in pupal stage. The granules present in the granulocyte were perhaps composed of polysaccharide, protein and lipid. In this stage the lipidous granules were especially rich.