Objective：This study was designed to assess whether inflation of the endobronchial cuff before lateral positioning would further secure a double-lumen endobronchial tube（DLT）and reduce movement. Methods：Sixty adult patients requiring one-lung ventilation were randomly enrolled into either the endobronchial cuff-inflated group（Group A）or the deflated group（Group B） during lateral positioning. Patients were intubated with a DLT under general anesthesia. Intubation depth was recorded. After the DLT was successfully intubated，the bronchial cuff was inflated in group A while the cuff was not inflated in group B when the lateral position was placed. Location of the double lumen was observed by fiberoptic bronchoscopy in the supine and the lateral position. The incidence and distance of the double lumen displacement in the two groups were recorded（defined as the distance from the tip of the trachea cavity of the double lumen to the trachea carina）. Results：A total of 28 patients（46.7%）in the two groups underwent double lumen displacement after lateral decubitus placement，including 10 patients in group A（33.3%）and 18 patients in group B（60.0%）. There were sigrificant differences between group A and group B （P=0.04）. The displacement distances of the two groups were （9.2±1.7） mm and （9.0±1.9） mm，respectively，with no significant difference（P > 0.05）. Conclusion：When placing the lateral position in thoracic surgery，the DLT is prone to displacement. Inflation of endobronchial cuff can significantly decrease the incidence of displacement of the DLT during lateral positioning.