By means of ultrathin section, negative staining and sucrose gradient ultra-centrifugation, a new baculovirus has been discovered and purified in lymphoid organs and such tissues as muscles of the shrimps which have been spontaneously attacked by diseases and artificially infected. With a diameter of 96-112 nm, this is the thickest baculovirus of shrimps ever known. In the center is the high-density nucleus. Between the capsid and the envelope is a broad space, which is not found in any of the baculoviruses of the prawns ever reported. On the surface of the purified nucleocapsid, there is a subunit of the spiral arrangement, which is also characteristic of this virus. It has not been observed and found in the epithelial cells of the livers, intestines and cheeks, which is quite different from the fact that prawn baculoviruses infect a certain epithepilial cell of the above-mentioned ones without exception. The viruses only multiplicate inside the core of target cells, which will not form occluded bodies or inclusion bodies. It is a new virus which has never been reported. It is called lymphoid cell nuclear baculovirus (LNBV).