Abstract: Background and Objective: Lannea microcarpa is widely used in traditional medicine against hypertension. This study evaluates the effect of aqueous extract of Lannea microcarpa (LMaq) on normotensive rats and its chronic antihypertensive effects in the L-NAME-induced hypertensive model. Materials and Methods: The effect of LMaq (5 and 25 mg kg–1), Captopril (5 mg kg–1) and NaCl 0.9% on arterial pressure were studied by daily oral administration in normotensive rats for 4 weeks. Daily oral administration of L-NAME (40 mg kg–1) for two consecutive weeks resulted in hypertensive rats. For evaluation of antihypertensive effects, hypertensive animals were then treated with either LMaq (5 or 25 mg kg–1) or captopril (5 mg kg–1) in combination with L-NAME for the next 2 weeks. Blood pressure parameters were measured by a tail-cuff system. Results: In normotensive rats, daily administration of LMaq did not have a significant effect on their blood pressure compared to that of the control group. Daily administration of L-NAME induces an average mean progressive increase in systolic blood pressure (SBP) from the 1st week (106.91±7.28 mmHg) to 171.16±0.41 mmHg after 2 weeks in LMaq and Captopril groups, respectively. In L-NAME-induced hypertensive rats, LMaq and Captopril significantly decreased their average mean SBP to 112.25±2.59 mmHg only after four days of treatment. Some significant modifications were noted for creatinine, alanine, etc., parameters but the autopsy revealed any change in the appearance of the noble organs. Conclusion: These results suggested that LMaq has significant antihypertensive effects in L-NAME-induced hypertensive rats comparable to those of Captopril.