Viral hemorrhagic septicemia virus (VHSV),the etiologic agent of viral hemorrhagic septicemia in salmonid，caused great loss in aquaculture industry.Nucleoprotein is an important protein for activation of host immunological reaction.The nucleoprotein gene of VHSV was amplified by reverse transcription-polymerase chain reaction (RT-PCR),and cloned into pET28a vector.The recombinant E.coli BL21 (DE3) containing pET28a-N was induced and the expressed protein was detected by SDS-PAGE and Western-blot.The nucleoprotein gene fragment was 1 221 bp in length.The 48 ku target protein was expressed successfully after induced by 1 mmol/L IPTG at 5 hours.But the protein was mainly in the form of inclusion bodies after SDS-PAGE detection.The inclusion bodies was refolded with 8 mol/L urea,and diluted in 0.01 mol/L PBS (pH=9.0).Western-blot analysis showed that the expressed production can be identified specifically by the goat anti-VHSV positive serum.