Background and objective: To investigate the acute toxicity of Produced Formation Water on the oxidative stress and biochemical parameters of Tilapia guineensis under semi-static conditions at a concentration of 100 to 700ml for 96 hours. Materials and Methods: The juvenile of Tilapia guineensis were exposed to different concentration of Produced Water, and their LC50 value of 223.10ml was calculated after 96-hour exposure period. The antioxidant enzyme profile investigated include: glutathione reductase, superoxide dismutase, glutathione peroxidase and catalase. Stress biomarkers such as protein, alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST) were also determined at 24-hour, 48-hour, 72-hour and 96-hour exposure periods. Results: Lipid peroxidation (MDA) showed significant (p<0.05) decreases in higher concentration and exposure period of 72-hour and 96-hour. Significant concentration-dependent increases (p<0.05) were observed in the liver function enzymes, Superoxide dismutase, Catalase and glutathione reductase when compared to the control. Glutathione peroxidase when compared to the control decreased significantly (p<0.05) in higher concentrations and 48 - 96hour. Conclusion: The changes in the hepatic antioxidant enzyme activities and serum metabolites were evident of oxidative damage induced by Produced Formation Water. This showed that the treated Produced water is toxic to the fish and regulatory agency in oil and gas industry should improve their effort to ensure they are treated efficiently before discharged into the aquatic ecosystems to prevent potential toxicity associated with it.