Background: Postoperative pulmonary problems from thoracic procedures are more likely to occur, which may lead to higher morbidity, a longer hospital stay, higher expenses, and a higher fatality rate. Objective: This study was done to compare efficacy of using either individualized or the conventional positive endexpiratory pressure (PEEP) for one-lung ventilation on postoperative pulmonary complications. Patients and Methods: This prospective randomized controlled study was done on 116 patients of age between 18 and 70 years with American Society of Anesthesiologists physical status II to Ш of either sex who underwent elective thoracic surgeries using one-lung ventilation. Patients were allocated randomly to either conventional PEEP group in which patients underwent thoracic surgeries using conventional PEEP (5 cmH2O) or individualized PEEP group in which patients underwent thoracic surgeries using individualized optimal PEEP which produces the best static lung compliance. Results:The incidence of postoperative pulmonary complications (PPCs) was lower in individualized PEEP group (12.1%) compared to conventional PEEP group (34.5%) with p (0.004). The most common complication incidence was lung collapse, which was greater in the conventional PEEP group (10.3%) than in the individualized PEEP group (27.6%). Arterial oxygen pressure/fraction of inspired oxygen (PaO2/FiO2) ratio was greater in the individualized compared to conventional PEEP group (p < 0.001). There were no significant differences in incidence of pneumonia, pleural effusion, pneumothorax, ARDS, or pulmonary embolism. Conclusion: Using individualized PEEP in patients receiving one-lung ventilation for thoracic surgeries resulted in decreased incidence of postoperative pulmonary complications, lower postoperative lung aeration score, better intraoperative respiratory mechanics, and oxygenation with no significant changes in hemodynamics.