Objective：This study aims 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 amino-terminal pro-brain natriuretic peptide （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 and 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.