Abstract: A nuclear polyhedrosis virus causing an epizootic disease was isolated from the body of Actias sdene ningpoana Felder in Nanjing region in 1979.This virus infringes skin, blood cells, fat bodies and tracheae of the larva, forming polyhedra in the cell nuclei.Under the electron microscope, the polyhedron is tetrahedral, hexahedral or of irregular shape, but the virus particle is bacilliform.According to the international classification system, it belongs to Baculovirus subgroup A. It is one of the species of nuclear polyhedrosis viruses (NPV). The present virus is here described in China for the first time. It is considred to be a new NPV.