This study aimed to investigate the effects of tramadol administration on some haematological and biochemical indices in rats. Tramadol was administered orally to rats for 28 days at a dose of 10 mg/kg body weight/day, 50 mg/kg body weight/day and 100 mg/kg body weight/day. Twenty-four hours after the last tramadol, blood, liver and kidney were removed from the animals after an overnight fast and analysed for their haematological and biochemical parameters. Results obtained revealed that tramadol administration significantly reduced the levels of white blood cells (WBC), red blood cell (RBC), haemoglobin and platelet count (PLT) while its resulted in non-significant changes in other haematological parameters examined when compared with control rats. Tramadol intake significantly increased plasma levels of alkaline phosphatase (ALP), aspartate aminotransferase (AST), creatinine and urea while its reduced total protein levels. Hepatic and renal thiobarbituric acid reactive substances (TBARS) levels were significantly increased by tramadol administration while levels of endogenous antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) were reduced. This study confirmed the risk of increased oxidative stress, hepatotoxicity and nephrotoxicity due to tramadol administration. Although tramadol is reported to be effective in pain management, its toxicity should be kept in mind.