The pathogenicity of viral hemorrhagic septicemia virus (VHSV) from olive flounder Paralichthys olivaceus was investigated with masu salmon Oncorhynchus masou fry. The cumulative mortality of fish challenged with FYeosu05 isolate at 106.5 TCID50/fish was 60%. No mortality was observed in fish challenged with the isolates at 105.5 TCID50/fish and in mock-challenged fish. The affected fish showed darkening of the body, expanded abdomen, pale gills and enlarged spleen. VHSV from 106.3 to 107.8 TCID50/g-tissue was re-isolated from the dead fish. These results suggest that the VHSV from olive flounder is pathogenic to masu salmon fry, although with low virulence.