Propolis, a honeybee product, has become popular as a food and alternative medicine. Its constituents have been shown to exert pharmacological effects, such as anticancer, antimicrobial, and anti-inflammatory effects. The present study was performed to investigate whether Brazilian green propolis exerts antihypertensive effects in spontaneously hypertensive rats (SHR) and which constituents are involved in its effects. Brazilian green propolis was extracted with ethanol and subjected to LH-20 column chromatography eluted with ethanol. The ethanol-eluted fractions at 10 mg/kg were administered orally to SHR for 14 d. Significant decreases in blood pressure were observed in fractions 6 and 7. The active constituents were purified and identified to be four flavonoids: dihydrokaempferide and isosakuranetin in fraction 6 and betuletol and kaempferide in fraction 7. These flavonoids at 10 mg/kg were administered orally to SHR for 28 d, and as a result, isosakuranetin, dihydrokaempferide and betuletol produced significant decrease in blood pressure, especially marked were the effects observed in the group that received isosakuranetin. Brazilian green propolis, fractions 6 and 7, and the 4 active constituents relaxed isolated SHR aorta in a concentration-dependent manner. Therefore, these finding suggest that the vasodilating action may be partly involved in the mechanism of antihypertensive effect. Hence, the ethanol extract of Brazilian green propolis and its main constituents may be useful for prevention of hypertension.