Hypertension management poses a challenge in developing countries, where poverty, illiteracy and poor nutrition combine to exacerbate the condition. The study was carried out to examine the active constituents of aqueous extract of Hibiscus sabbdariffa calyces' using LC/MS, together with evaluation of its in-vivo hypotensive properties upon using two different techniques in extraction. The obtained LC/MS chromatograms revealed the presence of difference in the constitution of both extracts HSMac, extracted with maceration, and HSDec extracted with decoction. The oscillographic technique was employed on a live rabbit to evaluate the in-vivo antihypertensive properties of the extract. In the in-vivo studies, the HSMac extract moderately reduced the mean arterial blood pressure (mmHg) of an anaesthesized normotensive rabbit from a control value of 110 (when normal saline was administered) to 90 at does 1g/kg, while the HSDec extract didn't shown any significance change on the mean arterial blood pressure. These findings corroborate the use of macerated H. sabdariffa calyces' extract as an antihypertensive agent in ethno-medicine.