The present study demonstrates the first discovery of a yellow head disease-like virus (YHDLV) in Penaeus japonicus that were diagnosed as white spot disease and describes the histological changes and the characters of the virus under electron microscopical observation. In histological studies, cells with basophilic inclusion bodies and hypertrophied nuclei were found in various tissues, including the lymphoid organ, interstitial hepatopancreatic tissue, cardiac tissue, gill tissue, connective tissue, cuticular epidermis and hematopoietic tissue. Transmission electron micrographs revealed the presence of rod-shaped, enveloped virions in the cytoplasm of the necrotic cells. The virus was 150-200 nm in length and 40-50 nm in width, but extraordinarily long viruses were also detected in the cells. The features of the YHDLV were very similar to yellow head disease virus of Penaeus monodon in Thailand.