Dark body disease has been causing a serious problem for Climbing perch, Anabas testudineus, cultured in freshwater intensive farming system recently. The disease outbreaks usually occur with prevalent from 40 percent to 100 percent. In a previous study, the causative agent of the dark body disease was identified as a virus parasited in the cytoplasmic location of host cells. The virus has symmetric shape structure with the. ,size of about 150 - 160 nm and is surrounded by a capsid layer. In this study, by utilizing a primer set designed with sequences same as sequences of the primer set specific for major capsid protein (MCP) gene of RSIV (Red seabream iridoviros), positive PCR products were observed in samples using DNA templates extracted from both naturally and experimentally infected fish. A phylogenetic analysis based on the partial MCP sequence revealed that the virus caused the dark body disease in Cimbing perch was clustered in the genus Megalocytiviros of the family lridoviridae and was refered as ATIV (Anabas testudineus iridoviros). These results also suggested that livers and kidneys should be suitable organs for rapid diagnosis of ATIV disease using PCR techniques as described in this study.