We investigated the effect of selenium (Sel), a trace element in diclofenac sodium (DCF), nonsteroidal anti-inflammatory drugs-induced hepatic and renal toxicities in adult rats. Five experimental groups namely control, DCF (10 mg/kg), Sel (0.125 mg/kg), DCF + Sel (0.125 mg/kg), and DCF + Sel (0.25 mg/kg) consisting of 10 rats each were orally treated for 7 consecutive days. Following killing, biomarkers of hepatic and renal toxicities, antioxidant enzyme levels, myeloperoxidase activity, nitric oxide levels, reactive oxygen and nitrogen species (RONS), and lipid peroxidation (LPO) were analyzed spectrophotometrically. Further, the concentration of tumor necrosis factor alpha (TNF-α) was assessed using enzyme-linked immunosorbent assay, and hematological indices: white blood cells (WBC), lymphocytes, and neutrophils and eosinophil counts. Results indicated that DCF-induced increases in biomarkers of hepatic and renal toxicity were significantly ( p < 0.05) lessened in serum of rats co-exposed to DCF and Sel in a dose-dependent manner. DCF mediated decrease in antioxidant status, and increases in RONS, LPO, and TNF-α levels were reduced ( p < 0.05) in the liver and kidney of rats co-exposed to DCF and Sel. Additionally, Sel reduced hematological abnormalities associated with DCF treatment. Light microscopic examination showed that the severity of histopathological lesions induced by DCF was lessened in rats co-exposed to DCF and Sel. Taken together, Sel supplementation mitigated DCF-induced oxidative stress, inflammation, and hematological abnormalities in the liver and kidney of treated rats.