Abstract Background Acute high-altitude exposure increases the risk of acute mountain disease (AMS) and high-altitude pulmonary edema. After the initial exposure to high altitude, mountain climbers are worried about whether they will develop AMS. At high altitudes, there are no accurate indicators to predict the near future occurrence of AMS. Objectives To investigate whether treadmill exercise stress echocardiography at high altitude can predict the occurrence of AMS, and to find out some powerful factors associated with the susceptibility to AMS. Methods 36 healthy lowlanders were taken by bus from sea level to an altitude of 3600 m the next morning, during which they rested overnight at an altitude of 2150 m. Treadmill exercise stress echocardiography was performed immediately upon arrival at 2150 m, and the 2018 Lake Louise Questionnaire Score was performed the next day when arrived at the altitude of 3600 m. Heart rate (HR) and blood pressure (BP) were monitored during stress echocardiography. Left ventricular (LV) ejection fraction and E/e’ were calculated at rest and immediately after exercise. Other right ventricular systolic function parameters and pulmonary artery pressure (PAP) were calculated at the same time, which included tricuspid regurgitation velocity (TRV), tricuspid annular peak systolic excursion (TAPSE), systolic PAP (SPAP), right ventricular (RV) dimension by 2D, RV fraction of area change (FAC), right ventricular outflow tract velocity time integral (RVOT VTI). Pulmonary vascular resistance (PVR) was calculated according to the formula: TRV/RVOT VTI*10+0.16. Mean PAP (mPAP) was calculated as the formula: sPAP*0.61+2. All subjects ascended to 3600m within 24 hours by bus. AMS was identified by 2018 Lake Louise Questionnaire Score. Univariable and multivariable logistic regression analysis assessed independent factors associated with AMS. Results At the altitude of 3600m, 13 of 36 subjects had AMS, which defined as AMS (+) group. And the rest was AMS (-) group. There were no significant differences in HR, BP, SO2 and LV systolic and diastolic function between the two groups (P > 0.05). No significant differences were noted at rest except for TV s' (P < 0.05). Immediately after exercise, TRV, TAPSE, SPAP, mPAP, PVR, and RV area at the end of systole were much higher in AMS (+) group (all P < 0.05). While FAC and TVs’/SPAP were much lower in AMS (+) group (P < 0.05). By multivariable logistic regression model, mPAP immediately after exercise was significantly correlated with AMS occurrence (OR =1.332, 95% CI: 0.669-0.993, P= 003). The cutoff value of mPAP to predict AMS was 32 mmHg (AUC: 0.831, specificity: 86.7%, sensitivity: 76.9%). Conclusions The mPAP immediately after exercise upon arrival at an altitude of 2150 m is a strong predictor of near future AMS, and treadmill exercise stress echocardiography is a simple and non-invasive tool to help mountain climbers avoid more severe mountain sickness.