Several enhancing proteins (enhancins) were isolated from the inclusion bodies of some insect viruses. The proteins can enhance the infection of NPV both in vitro and in vivo. There are two hypotheses about the mechanism of enhancement: disrupting the peritrophic membrane (PM ) and facilitating the penetration of virions or increasing the attachment and fusion between the virion envelope and the midgut cell membrane. The proteins are encoded by virus. The first enhancin gene has been cloned and sequenced.Since enhancins can shorten the life-span of infected larvae and increased the effectiveness of biopesticides，it will stimulate the widespread application of viral pesticides.