The aim of this study is to investigate whether extracts and semi-purified fractions obtained from Maytenus ilicifolia leaves have vascular effects in vivo.We tested the ethanolic supernatant of the infusion (ESI), and the ethanolic supernatant of the aqueous extract (ESAE) on the mean arterial pressure (MAP) and heart rate(HR) of anesthetized rats. Intravenous injection of ESAE caused a dose-dependent effect at 10, 20 and 30 mg/kg, reducing MAP by as much as 52.6 +/- 5.5 mmHg. Only the highest dose of ESAE (30 mg/kg) caused a significant reduction in HR during its hypotensive effect. The effect of ESAE was unchanged by atropine,propranolol, or bilateral vagotomy, but was significantly reduced (80%) in animals continuously infused with L-NAME. In addition, methylene blue and ODQ, as well as the potassium channel blockers tetraethylammonium,4-aminopyridine, and glibenclamide, impaired ESAE-induced hypotension. The ethyl acetate fraction(EAF) obtained from ESAE had a potency at least two times greater than ESAE in MAP, without causing any significant change in HR. The hypotension induced by EAF was circumvented by L-NAME, methylene blue andODQ, strongly reduced by tetraethylammonium and 4-aminopyridine (but not by glibenclamide), and abolished by association of these three potassium channel blockers. Chemical investigation revealed that flavonols, mainly catechin and epicatechin, as well as flavonol glycosides (mono- to triglycosides), and tannins, are the main components of this fraction. Our results demonstrate that preparations obtained from M. ilicifolia present a potent hypotensive effect in vivo, an event predominantly dependent on the nitricoxide/guanylate cyclase pathway.