Abstract Taiwan marine fish suffers the epidemic infection of iridovirus. In this research, infected fish of Epinephelus. lanceolatus was diagnozed by polymerase chain reaction. Transmission electron microscopy showed the morphology of viral particles from tissue lysate. The nucleotide sequence of major capsid protein (MCP) was compared to OSGIV, thereafter the novel virus from Epinephelus lanceolatus is named OSGIV-like iridovirus. By cloning expression of the MCP of TGIV and OSGIV-like, the MCP of 51 kDa was insoluable although minor virus-like substance was observed in TEM. Triton X-100 of 2.5% improved the solubility of protein to 30.95 £gg/£gl. Chloroform treatment enhanced the antibody-detection for the MCP of virus in the tissue. We inference that iridovirus MCP is associated with the envelope because of its hydrophobicity.