Studies have been conducted over the last decade to identify secondary metabolites from plants, in particular those from the class of alkaloids, for the development of new anti-Alzheimer’s disease (AD) drugs. The genusAlseodaphne, comprising a wide range of alkaloids, is a promising source for the discovery of new cholinesterase inhibitors, the first-line treatment for AD. With regard to this, a phytochemical investigation of the dichloromethane extract of the bark ofA. pendulifoliaGamb. was conducted. Repeated column chromatography and preparative thin-layer chromatography led to the isolation of a new bisbenzylisoquinoline alkaloid,N-methyl costaricine (1), together with costaricine (2), hernagine (3),N-methyl hernagine (4), corydine (5), and oxohernagine (6). Their structures were elucidated by the 1D- and 2D-NMR techniques and LCMS-IT-TOF analysis. Compounds1and2were more-potent BChE inhibitors than galantamine with IC50values of 3.51 ± 0.80 µM and 2.90 ± 0.56 µM, respectively. The Lineweaver–Burk plots of compounds1and2indicated they were mixed-mode inhibitors. Compounds1and2have the potential to be employed as lead compounds for the development of new drugs or medicinal supplements to treat AD.