Objective: Prehypertension is one of the primary causes of major cardiovascular events independent from other cardiovascular risk factors. The aim of the study was to evaluate the effect of therapeutic lifestyle modifications (LSMs) on cardiac diastolic function and aortic stiffness in prehypertensive subjects. Methods: This study designed as a prospective cohort study. Sixty-one prehypertensive adults were included in this study. The goals of LMS were weight loss of at least 5 kg in subjects with a BMI ≥25 kg/m2 and moderate-intensity physical activity at least 180 minutes per week. We evaluated left ventricular (LV) diastolic function and aortic stiffness parameters at baseline and after 6 months by conventional and tissue Doppler imaging (TDI) echocardiography. Statistical analyses were performed using Wilcoxon-signed rank test and the paired sample t test. Results: Transmitral early velocity (E), the ratio of E to transmitral late velocity (E/A), TDI diastolic early septal velocity (septal E), TDI systolic septal velocity (septal S), TDI early lateral velocity (lateral E), the ratio of septal E to TDI late septal (septal A) velocity (septal E/A) and the ratio of lateral E to late lateral (lateral A) velocity (lateral E/A) were found to be significantly increased after the LSMs (p<0.05 for all). The beta stiffness index was decreased (12.07 vs. 6.33; p < 0.001) and the aortic compliance (0.02 cm/mmHg vs. 0.05 cm/mmHg; p<0.001) and the aortic strain (3.28% vs. 7.02%; p<0.001) were increased significantly after the LSMs. Conclusion: LSMs improve conventional and TDI echocardiographic parameters and aortic stiffness measurements in subjects with prehypertension.