Ethnopharmacological knowledge provides useful information for experimental pharmacological studies. Based on this knowledge, this study was aimed at isolating the bioactive compound in Senecio serratuloides which is used in treating hypertension in Eastern Cape Province of South Africa. Senecio serratuloides was serially extracted using hexane, dichloromethane, ethyl acetate and methanol. The fractions were tested for their phytochemical constituents, antioxidant capacity and antihypertensive properties. Methanol fraction was subjected to thin layer and column chromatography for isolation of bioactive compound whose acute antihypertensive effects was determined. Ethyl acetate and methanol fractions had more phytochemicals, better antioxidant capacity and significantly (p<0.001) prevented increase in systolic and diastolic blood pressure. The bioactive compound (Estran-3-one, 17-(acetyloxy)-2-methyl-, (2à,5à,17á)-) isolated from the methanol fraction significantly prevented increase in blood pressure from the first to the fourth hour after treatment. Senecio serratuloides is a potential source of lead compounds for treating hypertension.