Background. Prolonged air leak is the most common postoperative complication following lung resection. Despite the huge number of researches concerning this problem, no consensus exists regarding the choice of the appropriate method of pleural space drainage after thoracoscopic surgery.Objective. To compare suction and water-seal regarding their influence on the incidence of prolonged air leak.Material and Methods. This prospective randomized trial included sixty patients who underwent VATS lobectomies on different diagnoses in the Center for Thoracic Surgery, Clinical Hospital no. 122 (St. Petersburg) from September 2018 until May 2020. The open-label randomized controlled trial involved two groups: control group (water-seal drainage) and suction group. Each group consisted of thirty patients. Ten patients were discharged with a Heimlich valve.Results. The incidence of prolonged air leak was 23%. Patients in the suction group had a higher duration of air leak than those in the control group (5.3 ± 1.3 vs 3.7 ± 0.9 days, р = 0.04). The number of air leak cases was slightly higher in the suction group (8 and 6 patients); however, the difference was not significant (р = 0.57). Both groups had no difference in the number of complications (р = 0.2). There were no cases of reoperation.Discussion. The advantage of water-seal is a lower risk of parenchymal defects. Suction may increase holes in visceral pleura, cause hyperexudation, leading to prolonged duration of drainage. At the same time, the use of suction may decrease residual pleural spaces, match visceral and parietal pleura, which may decrease the duration of air leak. A lot of studies on this issue was performed, however, their results are contradictory.Conclusion. Drainage of pleural space after VATS lobectomies may be safely performed with water-seal. In the case of increasing surgical emphysema or appearance of progressive dyspnea, suction should be applied