Abstract Background: Cytological examination of body effusion has an essential role in different tumor staging and research of malignancy. Objectives: It is to study the diagnostic effect of serum tumor markers in differentiation between benign and malignant pleural effusion. Materials and Methods: A retrospective research was done on 39 patients (28 male and 11 female with an age range of 50–77 years old). All samples undergo diagnostic thoracocentesis. The cutoff values of serum tumor markers (CEA < 5 ng/mL; CA125 <35 U/mL; CA19-9 < 37 U/mL; and CA15-3 < 31 U/mL). Results: Thirty-nine cases, resulting in 26 (67%) benign pleural effusions and 13 (33%) malignant pleural effusions, mean ± SD of age was higher malignant pleural effusion than benign type. The sensitivity of cytology was 33%. Malignant pleural effusion tended to have higher serum marker tumor concentrations. A comparison association between benign and malignant pleural effusion revealed statistically significant only in CEA. Most areas under the curve had moderate values that ranged between 0.6 for CA125, CA15.3, and other combined tumor markers, except for CEA, which had a good AUC (0.799). The best efficacy of a single tumor marker is CEA with a cutoff value of 2.05 ng/mL; at this cutoff value, the sensitivity, specificity, and accuracy were 69.2%, 88.5%, and 82.1%, respectively. Conclusion: Single serum tumor markers showed moderate sensitivity and low specificity; their combination does not result in to increase level of sensitivity and specificity to a good and dependent level for diagnosis of the malignant pleural effusion. Cytology and serum tumor markers have aided role in diagnosis. Thoracoscopy and pleural biopsy remain dependent diagnostic tools for malignant pleural effusion.