Abstract: A nuolear polyhedrosis virus was isolated from laboratory reared C. zao in BeiJing, 1985. Scanning electron microscopy showed that the polyhedrons were four-ateriographic sphere in shaps, with 1.4 to 2.2 u diameter. The vlrons were rod-shaped, approxiMately 57 × 257 nm, and singly embeded. The virus infected mainly the nuclei of the fat body cells, epithelia cells and tracheal cells, nerve tissue, and Halpighian tubules of the host. The virus was determined as a member of the Subgroup A of genus Baculovirus.