The susceptibility of larvae and juvenile koi carp (0–56 days post hatch; dph) against carp edema virus (CEV) was investigated by experimental infection with the immersion method using homogenized suspension from gill tissues of the diseased fish. ​Although no CEV mortality was occurred during the larval stage (0–7 dph), CEV-positive fish were found at all dph (positive rate 12–48%). ​In the juvenile stage (14–56 dph), the positive rate and mortality increased with dph. ​The positive rates and mortality were positively correlated with the total length of fish. ​The positive rates of the fish that were greater than 20 mm in total length exceeded 50% and the dead fish caused by CEV-infection were observed at 30 mm in total length or greater. ​These results indicate that the CEV susceptibility of larvae and juvenile koi carp increase with fish size rather than dph.