The present study was undertaken to investigate primarily the parasitism between cabbage worm, Artogeia rapae, and parasitoid wasp species. The study particularly focused on verification of the evidence which indicates the suppression of host immune reaction caused by virus-like particles (VLPs) of parasitoid wasps. Four parasitoid wasps of A. rapae were identified; Cotesia glomerata, Teromalus puparum, Eurypoma sp., Teprastichus sp. The parasitoid wasps oviposited repeatedly on the lateral intersegmental fold of the abdomen of the host larvae by injecting their ovipositor. Number of oviposition by the parasitoids increased in proportion to the volume of the host larvae. The capsule formation of A. rapae induced by mixing calyx fluids from C. glomerata with sephadex bead was significantly inhibited. In the larval hemocytes of A. rapae, considerable decreases of plasmatocytes were noticed. In addition, electron microscopic study clearly revealed VLPs in the calyx cells and lumen. VLPs are type of viruses identified in the hemocytes of A. rapae. VLPs were detected mostly in the plasmatocytes, although a few viruses were also observed in the granulocytes. They were predominantly present in the cytoplasm of plasmatocytes. The present result clearly demonstrated an important role of virus in the parasitism between A. rapae and C. glomerata. Therefore, it is highly possible to believe that virus is the principle factor for the establishment of the parasitism between A. rapae and their parasitoid wasps.