Fluoride is an environmental and industrial pollutant. It has already been reported that the accumulation of fluoride can alter the activities of some enzymes involved in the free-radical metabolism and also decrease the activities of some enzymes involved in the antioxidant defense system. In the present study, we have investigated the antioxidative properties of aqueous extract of the bark of Terminalia arjuna (TA) on sodium fluoride (NaF) induced oxidative damages in the livers and kidneys of Swiss albino mice. The mice were treated with 600 ppm NaF for one week in drinking water and the activities of antioxidant enzymes, like superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST), and the levels of non-protein thiol, reduced glutathione (GSH), along with lipid peroxidation in the liver and kidney, were determined. Fluoride administration significantly altered the levels of all of the factors compared to that of normal mice. Dose- and time-dependent studies suggest that the aqueous extract of the bark of TA showed optimum protective activity against NaF-induced oxidative damages at a dose of 40 mg/kg body weight for 10 days. Oral administration of the extract for the specified dose and time followed by NaF treatment (600 ppm) normalized the levels of the hepatic and renal antioxidant enzymes, GSH, and lipid peroxidation significantly to almost normal levels. The effects of a known antioxidant, vitamin E, and a non-relevant agent, bovine serum albumin (BSA), have also been included in the study. In addition, TA extract has been found to possess radical scavenging activity. Combining all of the data, the results suggest that TA might possess a protective role against NaF-induced hepatic and renal oxidative damages, probably via its antioxidant properties.