Eleven fish cell lines were compared for susceptibility to red sea bream iridovirus (RSIV). Cytopathic effect was produced in BF-2, CHSE-214, FHM, JSKG, KRE-3, RTG-2 and YTF cell lines among the cell lines examined. The titers of the virus on BF-2 and KRE-3 were higher than those on the other cell lines.The pretreatment of BF-2 and KRE-3 cells with polyethylene glycol (PEG) or addition of PEG to the sample increased the virus titers. RSIV replicated at 15°C, 20°C, 25°C and 30°C but not at 37°C. The suitable temperature for viral growth was 20°C or 25°C. The virus was sensitive to acid (pH 3), chloroform and ether and unstable to heat but stable to ultrasonic treatment and repeated freezing and thawing. Treatment with 5-iodo-2-deoxyuridine (IUdR) reduced the titers of the virus.