Background: The initial step in diagnosing pleural effusion is to distinguish between transudate and exudate. In establishing this distinction, numerous parameters, particularly the Light criteria, have been utilized; however, there are instances where inaccurate results may arise. This study examined oxidative stress markers that may contribute in distinguishing between exudate and transudate fluids. Materials and Methods: This study included 50 patients diagnosed with pleural effusion and 30 healthy individuals. The Total Oxidative Status (TOS) and Total Antioxidant Capacity (TAC) parameters were analyzed in pleural fluid and serum samples using the Erel technique on an Abbott Aeroset autoanalyzer in the biochemistry laboratory. Results: The fluid TOS and TAC values in patients with the exudate group were higher than those in the transudate group (p<0.005). The exudate and transudate group exhibited elevated serum TOS levels in comparison to the control group (p<0.005). The serum TAC level in the control group was higher compared to the transudate and exudate groups. The serum (OSI) values in patients with exudative and transudative effusions were elevated compared to those in the control group. Serum OSI levels were significantly higher in exudative patients compared to both transudative patients and the control group (p <0.001). Conclusions: Oxidative marker levels are significantly increased in exudative pleural effusions. In differentiating pleural fluid exudate from transudate, we determined that assessing the levels of TOS and TAC, utilized as oxidative stress indicators, may aid in diagnosis.