Three groups of spontaneously hypertensive rats were administered by gavage with distilled water (control group), low-dose green tea (LGT, 0.2 g/kg BW day) and high-dose green tea (HGT, 1.0 g/kg BW day) for 4 weeks, during which systolic blood pressure (SBP) was measured weekly by non-invasive tail-cuff method. At the end of experiment, left ventricular hypertrophy index (LHVI) and plasma biochemical indicators were determined, and ultrastructures of myocardium and aortic vascular smooth muscle cells were observed by transmission electron microscopy (TEM). The results show that green tea gavage suppressed the increase in SBP, along with decline in levels of plasma nitric oxide, aldosterone, malondialdehyde, and LHVI, but increased levels of plasma creatinine, calcitonin gene-related peptide, and glutathione peroxidase in a dose dependant manner. Green tea had no effect on plasma total cholesterol. TEM shows that green tea gavage protected mitochondria of left ventricular myocardium and aortic vascular smooth muscle cells from damage.