A granulosis virus was isolated fiom the diseased riceleaf rollers, Cnaphalocrocis medinalis Guenee （CmGV）. Under electron microscope the capsules appear oval in shape and measuie about 350—500nm in leangth by 200—300nm in diameter. The crystalline lattice of the protein crystal reveals three highly regular patterns, the linear, the square and the rhombus. The linear pattein consists of a series of equally spaced lines across the entire capsule and the lines have a center to center spacing of 55. The genome of CmGV is DNA. The DNA consists of closed circular molecules; some of them present a superhelix in structure with molecular weight of 71-74×10,6, daltons. The infectivity of the virus in laboratory was very tow when the larvae were fed with CmGV alone; but the infectivity was grealy enhanced when the larvae were fed with CmGV and Prodenia litural NPV together. This paper also presents the cytopathetic changes in the tissues of the diseased larvae after they are mixed infected with 2 viruses and also their morphogenesis in the mixed infected cells. The fat body, the epidermis, the midgut epithelium and the tracheal matrix are the chief tissues attacked. Numerous capsules have been seen in the hemocytes. lt was shown that sometimes both viruses replicated simultaneously in one cell, but in most cases one virus replicated only in one cell while the other virus replicated in other neighboring cells.