Abstract Introduction: Selenium nanoparticles (SeNPs) are a promising modality of treatment for various oxidative stress induced and inflammatory diseases. Tramadol (TD) has become the most commonly prescribed opiate with a high liability for addiction, predisposing the liver to oxidative stress induced hepatotoxicity. Aim: This study aimed to clarify the impact of SeNPs on biochemical and histological alterations induced by TD. Materials and Methods: Sixty rats were divided into four groups: Group I: (Control group) included 15 rats, Group II: (SeNPs group) 5 rats received intraperitoneal (i.p.) injections of SeNPs. Group III: (TD group) 20 rats received i.p. injections of TD. Group IV (SeNPs + TD) 20 rats received SeNPs one hour before each administered dose of tramadol. Liver specimens were carefully harvested and processed for biochemical, light and electron microscopic studies, morphometric and statistical analysis. Results: Tramadol administration resulted in reduced antioxidant enzyme activities and elevated liver enzyme and malondialdehyde levels. Furthermore, dilated congested central veins and sinusoids, swollen hepatocytes with shrunken darkly stained nuclei and rarified cytoplasm, inflammatory infiltrations, and congested portal veins were observed. This was associated with depletion of intracellular glycogen and proteins, increased Bax and Glial fibrillary acidic protein expression, and collagen bundle deposition near hepatic stellate cells, between hepatocytes, and in the spaces of Disse. Administration of SeNPs significantly ameliorated these findings probably due to its antioxidant properties. Biochemically, a significant increase in antioxidant enzyme activities and decrease in liver enzyme and malondialdehyde levels was observed. Liver histology also improved with a significant increase in hepatocyte glycogen and protein content. Additionally, Bax and GFAP expression were comparable to that of the control group. Conclusion: SeNPs were hepatoprotective against oxidative stress induced by TD.