The phagocytosis of five established cell lines, IPLB-Sf-5-5C, UCR-Se-1, NTU-Sl-1A, NTU-Pn-HH, and IPLB-Ld652Y was examined by fluoresbrite carbosylate particle uptake. The phagocytic action of the Sf-5-5C cells was highly efficient compared to other cells, while Pn-HH cells showed no phagocytic action. Sf-5-5C, Se-1 and Sl-1A engulfed readily the OBs of AcMNPV, a virus to which they are susceptible, while they did not engulf the OBs of the non-susceptible virus, PenuNPV. These findings suggested that these insect cell lines would be useful for studying phagocytosis in vitro. Thus, Sf-5-5C cells were selected for the advanced study of phagocytosis. Three types of Sf-5-5C cells, non-basophilic cells, light basophilic cells and basophilic cells, were distinguished by morphology, toluidine blue staining, and electron microscopic staining. The non-basophilic cells acted as the main phagocytic cells in OB uptake, while the phagocytic activity of the light basophilic cells was weak. Inside the phagosome, the OBs were digested in the cytoplasm. The titration of AcMNPV in the culture media of Sf-5-5C cells after OB uptake was examined. The results implied that AcMNPV may be released from the engulfed OBs.