Abstract: The relationship between the survival rate, developmental duration of Microplitis sp. in Spodoptera litura larvae and time of exposure of the host larvae to virus, the inoculation virus concentration were investigated to determined if parasites which emerged from virus-infected S.litura larvae had normal survive, and if the parasites could sever as the vector for S.litura nuclear polyhedrosis virus (SlNPV). There was no significant difference in time that parasites spent in virus-infected larvae and healthy one, indicating the SlNPV did not affect the developmental period of Microplitis sp. Parasite larvae in hosts exposed to virus after parasitization compmeted their development before their hosts died of virus infection. The proportion of parasites survived varied with the inoculation virus concentration and the time of exposure of the host larvae to virus, the percent of parasites survived increased as the time between host parasitization and host virus exposure increased, and decreased as the inoculation virus concentrations increased. The female parasites which developed or oviposited in virus-infected hosts, and manually contaminated the ovipositor of the females with virus suspension could all carry infective doses of the virus, and transmit virus from infected larvae to healthy one through ovipositor. A female parasite which developed or oviposited in virus-infected hosts transmitted infective doses of the virus to an average of 2.14, 2.45 healthy host larvae exposed to it respectively. A female parasite from the cocoon contaminated with SlNPV of different virus concentration could transfer infective doses of the virus to an average of 1.45 healthy host larvae.A female parasite exposed to the mixture of different virus concentration and 10% honey-water solution could also transmit virus to an average of 0.94 larva.