Excessive tracheal tube cuff pressure can cause postoperative complications; however, the variations in the double-lumen tube cuff pressure in lung surgery have not been investigated. This study aimed to determine the incidence and variations in excess double- lumen tube cuff pressure during one-lung ventilation. A prospective observational study. Single secondary-care hospital. Patients aged ≥18 years scheduled for elective lung surgery using a left-sided double-lumen tube. None MEASUREMENTS AND MAIN RESULTS: Each cuff of the double-lumen tube was connected to a pressure transducer, and the cuff pressure was continuously measured. The excess cuff pressure and its duration (%) were defined as ≥22 mmHg, and the ratio of the duration of excess cuff pressure to the duration of one-lung ventilation, respectively. In total, 147 patients were included in the final analysis. Eighty patients (54.5%) developed cuff pressure elevation in either cuff and 28 patients (19%) in both cuffs. Younger age, male sex, and left-sided surgery were associated with elevated bronchial cuff pressure. Concurrently, younger age, maximal peak inspiratory pressure, and obstructive respiratory dysfunction were associated with an elevated tracheal cuff pressure. A duration of excess cuff pressure >50% in either cuff was found in 34 patients (23%), and both cuffs in 5 patients (3.4%). The correlation between the duration of tracheal and bronchial excess cuff pressure was poor. A high incidence and long duration of excess tracheal and bronchial cuff pressure were observed during one-lung ventilation for lung surgery.