Introduction: Hypertension is one of the most common human disease and a major risk factor for cardiovascular disease. Angiotensin converting enzyme inhibitor (ACE!) drugs, including captopril, is used for treatment of hypertension frequently. In this study BLOOD PRESSURE CONTROL parameters of captopril was compared between Iranian and foreign types by 24-hours ambulatory BLOOD PRESSURE monitoring.Methods: Onehundred and twenty five patients with mild to moderate primary hypertension were included in a randomized double blind clinical trial. After a wash out period, patients performed a 24-hours ambulatory BLOOD PRESSURE monitoring, and then treated by one of the three Iranian-types (Iran Dam, Lorestan and Dam Paksh), foreign type captopril and placebo randomly. After Four weeks treatment, BLOOD PRESSURE monitoring was performed again. Statistical analysis was done with ANOVA and T-Student test.Results: The study showed that all types of these drugs reduced BLOOD PRESSURE significantly related to placebo (P<0.05). No significant difference was detected in magnitude, duration and maximum effect between them (Except for non-statistically significant longer effect in foreign type). In foreign type, time to reaching maximum effect was shorter significantly than Iranian types.Discussion: This study showed that all types of Iranian captopril have similar anti-hypertensive quality, and according to no greater effect in foreign type, so it's not logical to use it because of greater cost to patient and community.