Possible preventive or therapuetic effects of fuciodan, which has antioxidant properties and was administered together with gentamicin (GM) made up nephrotoxicity through giving GM to the rats, have been searched. The rats used in this study were randomly grouped in three: control, GM (80 mg/kg/day/i.p GM was administered for 8 days), GM+fucoidan (80 mg/kg/day/i.p GM for 8 days + fucoidan 100 mg/kg/day/ for 8 days were administered with intra-gastric gavage) groups. Blood and tissue samples were taken 24 hours after the 8 days trial period. Besides determining plasma creatinine, BUN, sodium, potassium, chloride levels in auto-analyser, whole blood glutathione, plasma MDA and AOPP levels were analyzed spectrophotometrically. The highest plasma creatinine, BUN, potassium, AOPP and MDA levels were found in the GM group. It was determined that while the levels of creatinin (p<0.01), BUN (p<0.05), potassium (p<0.05), AOPP (p<0.01), MDA (p<0.01) in GM+fucoidan group were decreasing with regard to those in GM group, chloride levels were rising (p<0.05). The study revealed the nephroprotective effect of fucoidan. These findings suggest that fucoidan administration together with GM may attenuate renal dysfunction and structural damage through the reduction of oxidative stress in the kidney.