In order to detect different species of iridescent virus from largemouth bass,two pairs of specific primers,named Rana-mcp and Mega-mcp with predicted products of 475 bp and 262 bp,were designed from sequences of major capsid protein (MCP) gene from Ranavirus and Megalocytivirus, respectively.The reaction conditions of the duplex PCR were optimized,and the specificity and sensitivity were further studied.The limit DNA of the duplex PCR for Ranavirus and Megalocytivirus were 6.5 pg and 14.5 pg,respectively.Using duplex PCR and sequencing methods,15 clinical samples were tested and 5 positive samples from Ranavirus infection and 1 positive sample from Megalocytivirus infection were detected.The developed duplex PCR method based on MCP gene could be used for rapid diagnosis and epidemiology investigation on iridescent virus disease of cultured largemouth bass.