Background: Double-lumen tubes (DLTs) are widely used in thoracic surgery to achieve one-lung ventilation. International recommendations suggest tube size selection based on height and sex (39 41 Fr for males ≥160 cm, 35–37 Fr for females ≥150 cm). However, in Mongolian practice, applying these standards often leads to oversized tube use and related complications. Objective: To compare international standards for DLT size selection with body height and sex in Mongolian patients. 10 Methods: A cross-sectional study was conducted among patients who underwent esophagectomy with left-sided DLT placement at the National Cancer Center of Mongolia between 2018 and 2023. Data included age, sex, height, and DLT size. Statistical analysis was performed using chi-square and t-tests, with p < 0.05 considered significant. Results: A total of 211 patients were analyzed (58.8% male, 41.2% female). Among males, 170 cm patients received 37 Fr in 90% of cases (p < 0.001). Among females, 160 cm patients either 35 Fr or 37 Fr (p < 0.001). Tube size also differed significantly by sex (p < 0.001): 68.5% of males received 37 Fr, while 83.9% of females received 35 Fr. Conclusion In Mongolian clinical practice, DLT sizes are generally chosen smaller than those recommended by international standards, based on sex and height. All patients in the study achieved successful one-lung ventilation and favorable surgical conditions, indicating that international standards may not be fully applicable to the Mongolian population. Moreover, the study highlights that while DLT size selection correlates strongly with height in males, the association is weaker in females. Therefore, reliance solely on height and sex may be insufficient, and additional biometric and anatomical parameters should be considered for optimal tube selection