Physical characteristics of a nuclear polyhedrosis virus isolated from Spodoptera litura was examined under the electron microscopes. A polyhedron was 1.9 ${mu}{ extrm}{m}$ in average with the range of 1.3 ${mu}{ extrm}{m}$ to 2.3 ${mu}{ extrm}{m}$ in size and showed tetragonal in outline. Virions released from polyhedra after alkaline treatment were separated into nine bands through sucrose linear density gradient centrifugation, but the bands were depended on the number of rod-shaped nucleocapsids in an envelope. Nucleocapsids were embedded in a virion, so called multiple embedded nuclear polyhedrosis virus (MNPV), under the electron microscope with the size of 40~50 nm by 380~440 nm.