Abstract: A cytoplasmic-polyhedrosis virus causing a spectacular epizootic disease has been isolated from the body of pine caterpillar(Dendrolimus tabulaeformis Tsai et Liu)in Sept.1977 in Liaoning Province. This virus infringes Cylindrate cells of mid-gut(chylific),forming polygonal bodies in the cytoplasm. The image of the polygonal body is shaped like a dodecahedron in stereoscopic view and like a regular hexagon in surface view. The image of virion is also shaped like a hexagon in plance with a diameter of 57—63 mμ. According to the international classification system,it should belong to Reoviridae.It is one of the species of Cytoplasmic-polyhedrosis viruses(CPV).Based on the investigation and information available,it is considered to be a promising biologicalcontrol agent to control pine caterpillar in China.