Baculoviruses and parasitoids are important biological control factors of insects in integrated pest management. Microplitis bicoloratus Chen (Hymenoptera: Braconidae: Microgastrina) is a solitary endoparasitoid of beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) larvae. M. bicoloratus parasitized first to third instars of S. exigua and most effectively parasitized second instars. The survival rate of parasitoids emerging from S. exigua multiple nucleopolyhedrovirus (SeMNPV)-infected hosts decreased with increasing SeMNPV doses at second to fourth instars. In addition, the mortality rate of the host was > 80% when coinfected with SeMNPV and M. bicoloratus, regardless of virus doses or the timing of virus treatment. Occlusion body production was significantly reduced in parasitized hosts. A comparison of host weights showed that hosts coinfected with SeMNPV and M bicoloratus were significantly lighter than those infected with SeMNPV alone, suggesting that the decrease in virus yield resulted from a reduction in larval growth. The viral genome copy number in parasitized host was significantly lower than that in nonparasitized host at 48 and 72 h postinfection. These results suggest that SeMNPV and M. bicoloratus are compatible as S. exigua control agents.