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 end-expiratory 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.