Objective This study aims to evaluate the effect of the pressure-controlled ventilation-volume guaranteed (PCV-VG) mode on postoperative pulmonary complications, oxygenation, and ventilator-associated lung injury in preschool children undergoing thoracic surgery. Methods This prospective randomized controlled trial included 71 preschool children undergoing thoracic surgery between April 2020 and June 2021. Participants were randomized in a 1:1 ratio using a computer-generated allocation scheme into the PCV-VG group (n=36) and the conventional volume-controlled ventilation (VCV) group (n=35). All perioperative ventilation followed lung-protective ventilation strategies, with the PCV-VG group receiving PCV-VG mode and the VCV group receiving VCV mode. The primary outcome was the incidence of pulmonary complications within 72 hours postoperatively. Secondary outcomes included intraoperative respiratory mechanics, arterial blood gas analysis, circulatory parameters, mechanical ventilation duration, and hospital stay. Results The incidence of postoperative pulmonary complications in the PCV-VG group (3/36, 8.3%) was significantly lower than that in the VCV group (10/35,28.6%, P = 0.035 ) During one-lung ventilation (OLV), the PCV-VG group demonstrated significantly lower peak airway pressure [OLV 30 minutes: 20 (18,22) cmH2O us. 25 (23,27) cmH2O; end of OLV:17 (15,18) cmH2O vs. 20 (18,22) cmH2O; P < 0.001 ] and lower respiratory resistance [OLV 30 minutes: 48.7±10.3 s. 60.5 ±13.3; P = 0.027 ], along with better lung compliance [OLV 30 minutes:6.0 (4.0,7.0) mL/cmH2O vs. 5.0 (4.0,6.0) ml/cmH2O; P = 0.021 ; end of OLV:8 (7.0,9.0) mL/cmH2O vs. 7 (6.0,8.0) mL/cmH2O; P = 0.041 ] . Oxygenation in the PCV-VG group was also superior to the VCV group [OLV 30 minutes: 136.4 (120.4, 165.0) mmHg vs. 100.0 (89.4,137.5) mmHg; end of OLV: 190.2 (179.3,202.2) mmHg vs. 176.8 (142.1,189.8) mmHg, P < 0.05 ] . Additionally, the PCV-VG group had shorter postoperative mechanical ventilation duration [97.5 (70.0,137.5) minutes rs. 120 (95.0, 140.0) minutes; P = 0.04 ] and hospital stay [7 (5,9) days vs. 8 (7,15) days; P = 0.024 ] . Conclusions The PCV-VG mode significantly reduces postoperative pulmonary complications, lowers airway pressure during OLV, and improves oxygenation in preschool children undergoing thoracic surgery. PCV-VG can be considered the preferred mechanical ventilation strategy for such procedures. [ABSTRACT FROM AUTHOR]