Since the serious attention has given to the use of insect pathogenic viruses for the biological control of insect pests, we tried to isolate the infectious virus from the diseased larvae of fall webworm, Hyphanlria cunea, which is a pest of roadside trees and diciduous trees. The isolated virus was able to succeed in replication of H. cunea virus in an established insect cell line derived from the ovary of adults of cabbage looper, Trichoplusia ni. Based on pathological and morphological properties (by EM pictures), it was found that this virus is included in nuclear polyhedrosis virus (Baculovirus subgroup a). The polyhedral inclusion bodies ranged from 0.6 to 2.5 ㎛ in diameter and rodshaped nucleocapsids were enveloped in multiples of up to 22. Polyhedral protein preparations from H. cunea NPV and A. California NPV (reference virus) were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In SDS-PAGE, the major protein component ranged from 28,000 to 29,000 dalton among the isolates. It was also found that the genome of H. cunea was DNA.