This study was performed to investigate the pathphysiological side effects of chloramphenicol (CAP) on olive flounder, Paralichthys olivaceus. 150 mg/kg/bw/day of CAP was orally administered forcedly to flounder for 4 days and then the flounder was monitored for 11 days. The level of hematocrit was significantly decreased from 2 day to 3 day of CAP treatment in CAP-treated group. The levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and gamma glutamyl transferase (GGT) were slightly increased during the treatment of CAP and gradually decreased after the treatment of CAP. The levels of blood urea nitrogen (BUN) and creatinine kinase (CK), although not significant, were slightly increased during the treatment of CAP. The level of lactate dehydrogenase (LDH) was not changed during the treatment of CAP but slightly increased after the treatment of CAP. However, no histopathological changes were observed in various organ after the treatment. From these results, it is suggest that CAP can evoke several side effects on haematopoietic organs in olive flounder