Four new naphthylisoquinoline alkaloids, ancistrotectoriline A (1), ancistrotectoriline B (2), 6-O-methyl-4'-O-demethylancistrocladine (3), and 6-O-methyl-4'-O-demethylhamatine (4), were isolated from the stems and leaves of Ancistrocladus tectorius, collected from Hainan Province, Southern China. Their structures were elucidated using MS and NMR methods.