Objective: To assess the cardiac structure and function in patients of heart failure with mid-range ejection fraction (HFmrEF) by speckling tracking echocardiography after 3 months Sacubitril/valsartan treatment. Methods: A total of 35 patients with HFmrEF (EF range: 40%-49%) and New York Heart Association (NYHA) class Ⅱ～Ⅲ were enrolled in this study from Jul 2020 to Jan 2021. In these patients, echocardiographic assessments were performed at the baseline and after 3 months sacubitril/valsartan therapy. The left ventricular (LV) global longitudinal strain (LVGLS) and the time to the peak strain were evaluated by using speckling tracking, the LV end-diastolic volume index (LVEDVI), LV end-systolic volume index (LVESVI), LV ejection fraction (LVEF) and left atrial volume index (LAVI) were acquired by Simpson’s method. Color and tissue Doppler ultrasound were utilized to get the ratio of early transmitral Doppler velocity/early diastolic annular velocity (E/e’). The level of serum NT-proBNP was determined by electrochemiluminescence immunoassay method. Results:After the treatment, the NYHA function capacity class improved significantly (P=0.008) and the median NT-proBNP concentration decreased significantly（P<0.001). The LVGLS increased markedly compared with the baseline, and the time to peak longitudinal strain reduced significantly than the baseline (P<0.001). There was a modest improvement in the LVEF (P=0.001). The LVEDVI, LVESVI decreased significantly compared with the baseline (P<0.001). However, there was no significant change for LAVI and the E/e’ (both P>0.05). Conclusion: In HFmrEF patients, 3 months sacubitril/valsartan therapy could induce benefit on the left cardiac structure and function. Strain analysis based on speckling tracking echocardiography may act as a useful tool for assessment of the left ventricle remodeling in these patients.