Purpose: To investigate the protective effects of dimethylsulfoxide (DMSO) on chronic oxidative stress in the liver, kidney and serum with biochemical parameters such as malondialdehyde (MDA), advanced oxidation protein product (AOPP), catalase, glutathione (GSH), andfree-thiols (F-SH). Methods: Thirty Wistar albino female rats were randomly divided into 3 groups: group I (control, n=10), group II (irradiation-alone group, n=10) and group III (DMSO and irradiation group, n=10). Rats in groups II and III were irradiated with a single dose of 6 Gy to the entire liver and right kidney. Group III received DMSO 4.5 g/kg by intraperitoneal injection 30 min before irradiation. At the end of the 24th week, the rats were sacrificed and their trunk blood, kidney and liver tissues were collected. Results: Group II rats showed increased levels of lipid peroxidation and protein oxidation, with decreased GSH, F-SH and catalase levels in all specimens when compared with group I. Serum and kidney MDA and AOPP levels were significantly lower in group III when compared with group II. However, serum and kidney GSH and F-SH levels were significantly higher in group HI when compared with group II. The additive effect on catalase was seen only in the serum. Conclusion: DMSO is a protective agent on chronic oxidative stress in the serum and kidney tissue. No oxidant or antioxidant effect of DMSO in the liver was seen. © 2012 Zerbinis Medical Publications.