We have evaluated the antihypertensive effect of several flavonoid extracts in the spontaneous hypertensive rat model (SHR). Treatments were carried out for 6 and 12 weeks in two groups of SHR rats which received Apigenin, Lemon Extract, Grapefruit + Bitter Orange (GBO) extracts and Cocoa extract. Captopril was used as a positive control in the SHR group treated for 6 weeks (SHR6) and Diosmin was used as the industry reference in the SHR group treated for 12 weeks (SHR12). Captopril and GBO extracts significantly reduced the elevated blood pressure of the SHR6 animals, but none of the extracts was effective in the SHR12 group. Apigenin, LE, GBO and captopril also ameliorated nitric oxide-dependent and independent aortic vascular relaxation and elevated plasma and urinary excretion of nitrites, only in the SHR6 group. Kidney and urinary TBARS were also significantly reduced by GBO in the SHR6 rats. Apigenin also improved vascular relaxation in the SHR12 group and all the flavonoids studied reduced urinary TBARS excretion and proteinuria. Vascular abnormalities such as lumen/wall ratio in coronary arteries and thoracic aorta were moderately improved by these treatments in the SHR6 group. In conclusion, the flavonoids included in this study, especially apigenin, LE and GBO improved vascular vasodilatory function of young adult SHRs but only the GBO-treated rats benefited from a reduction in BP. These extracts may be used as functional food ingredients with a moderate therapeutic benefit, especially in the early phases of arterial hypertension.