This study examined the efficacy of silver nanoparticles colloid (AgNPC) in reducing the pathogenicity of the Bombyx mori L. (Lepidoptera: Bombycidae) nuclear polyhydrosis virus (BmNPV) in silkworms. We found that the survival rate of the infected silkworms improved significantly, from 22 to 67%, following treatment with AgNPC. However, AgNPs caused clumping of hemocytes in vivo and this was associated with slight weight loss and reduced cocoon size in the treated silkworms. The adherence of silver nanoparticles to the virus or hemocytes caused them to aggregate. In addition, by catalyzing the generation of free radicals, silver nanoparticles can perforate and break up the virus capsids, proteins, and DNA of the BmNPVs, thus restraining their pathogenicity and improving the survival capacity of infected silkworms.