Two new aporphine alkaloids, isofiliformine ( 1) and cassythic acid ( 3), along with 22 known compounds were isolated from whole herb of Cassytha filiformis. Cassythic acid ( 3), cassythine ( 4), neolitsine ( 7), and dicentrine ( 8) had potent vasorelaxing effects on precontracted rat aortic preparations with mean IC 50 values between 0.08 and 2.48 microM. Compounds 1, 1,2-methylenedioxy-3,10,11-trimethoxyaporphine ( 2), (-)- O-methylflavinatine ( 10), (-)-salutaridine ( 11), isohamnetin-3- O-beta-glucoside, and isohamnetin-3- O-rutinoside exerted moderate vessel-relaxing activities with IC 50 values from 16.50 to 32.81 microM at the test concentrations.