Five new protopine-type alkaloids, 3,5-di-O-methylconstrictosine (1), 5,6-dihydro-3,5-di-O-methylconstrictosine (2), 5,6-dihydroconstrictosine (3), constrictosine (4), 3-O-methylconstrictosine (5), and a novel 8-benzylberberine-type alkaloid, (-)-8 beta-(4'-hydroxybenzyl)-2,3-dimethoxyberbin-10-ol (6) were isolated from the aerial parts of Aristolochia constricta. Their structures were elucidated by physical and spectroscopic data. The results of our pharmacological experiments indicated that MeOH extract, its partially purified fraction VI and the protopine derivatives constrictosine 1-5, significantly reduced, in a dose dependent manner, the electrical, acetylcholine, and histamine contractions of the isolated guinea-pig ileum.