Twelve isoquinoline alkaloids including two new nitro-containing tetrahydroprotoberberines, (-)2,-9- dihydroxyl-3,11-dimethoxy-1,10-dinitrotetrahydroprotoberberine (1) and (+)-4-nitroisoapocavidine (2), were isolated from the whole plant of Corydalis saxicola Bunting. The structures of the new compounds were established by spectroscopic analysis and chemical evidence. The inhibitory activity of these isolates against cholinesterase and canine parvovirus were evaluated. Compounds 1 and 1a, (+)-1-nitroapocavidine (5), berberine (8), palmatine (9), dehydrocavidine (10), and sanguinarine (11) showed potent inhibitory activity against acetylcholinesterase with IC(50) values of less than 10 mu M, while only compound 1 possessed weak activity against canine parvovirus. Structure-activity studies demonstrated that the nitro substituents at ring A in the tetrahydroprotoberberines led to an increase in the anti-acetylcholinesterase activity.