The study was aimed to evaluate the possible effects of dexamethasone on oxidant/antioxidant status in kidney tissues of rats administered mercuric chloride (HgCl2). Thirty male Wistar-albino rats were enrolled in this study. Rats were divided into 4 groups: G1 (n=7) underwent no therapy (control group), G2 (n=8) received HgCl2 + physiological saline, G3 (n=7) dexamethasone (DM) + physiological saline and G4 (n=8) received HgCl2 + DM. HgCl2 was injected subcutaneously into rats in the G2 and G4 on the first day of the study. Dexamethasone was injected intraperitoneally into rats in the G3 and G4 for 3 days. Malondialdehyde (MDA) levels, catalase (CAT), glutathione peroxidase (GSH-Px), xanthine oxidase (XO) and superoxide dismutase (SOD) activities were evaluated in the kidney tissues. Serum creatinine levels were also measured. Xanthine oxidase activity was increased in the G2 compared to the control group. Catalase activity in the control group was significantly higher compared to the other groups. In the histopathological examination of kidneys, there was a tubular degeneration in G2 and G4. It was concluded that HgCl2 administration may cause oxidative stress through increasing XO and decreasing CAT activities. Dexamethasone injection may partially protect the rat kidneys against oxidative reactions by preventing the increase in XO activity (Tab. 1, Ref. 33).