Abstract: Objective To investigate the effects of aerobic exercise at prehypertension stage on the blood pressure,cardiac functions and pathological alterations as well as cardiac angiotensin converting enzyme 2signaling in spontaneously hypertensive rats（SHR）,and to elucidate the potential mechanisms. Methods Five-week-old male SHR（n=24）and normotensive Wistar Kyoto rats（WKY）（n=24）were randomly divided into sedentary（S）and exercise training（E）groups. The training rats ran on a treadmill at a low to middle intensity for 16 weeks. After completed the exercise protocol,blood pressure,systolic and diastolic functions of the left ventricle,left ventricular hypertrophy and fibrosis were evaluated. Real-time polymerase chain reaction（PCR）and Western blot were used to detect the mRNA and protein expressions of myocardial angiotensin converting enzyme 2（ACE2）and Mas receptors,respectively. The angiotensin-（1-7）Ang（1-7）levels of the left ventricle were determined by enzyme linked immunosorbent assay（ELISA）. Results 16-week exercise training significantly decreased systolic blood pressure（P＜0.01）and the left ventricular end diastolic pressure（LVEDP）（P＜0.01）,enhanced the maximal fall velocity of left ventricular pressure（-dp/dtmax）（P＜0.01）in SHR. Exercise training also reduced the left ventricular mass（LVM）,the left ventricular collagen volume fraction（CVF）and perivascular collagen volume fraction（PVCA）in SHR（all P＜0.05）. 16-week exercise training greatly upregulated cardiac mRNA and protein expressions of ACE2 and Mas receptors（all P＜0.01）and increased myocardial level of Ang（1-7）（P＜0.001）in SHR.In WKY,exercise training did not result in the hypertrophy of left ventricle,but upregulated the mRNA expression of ACE2 and Mas receptors of the left ventricle（all P＜0.05）and increased cardiac Ang（1-7）level（P＜0.05）in WKY. Conclusion Early exercise training at prehypertension stage significantly decreases blood pressure,improves the left ventricular function and attenuates myocardial fibrosis,which are associated with the enhanced functions of cardiac ACE2-Ang（1-7）-Mas axis in SHR.