Phytochemical investigation of the bark of Guatteria olivacea R. E. Fries (Annonaceae) led to the isolation and identification of ten isoquinoline-derived alkaloids, including three phenanthrenes, atherosperminine, argentinine, and atherosperminine N-oxide; three aporphines, asimilobine, puterine, and discoguattine; two oxoaporphines, liriodenine and oxoputerine; and two tetrahydroprotoberberines, corypalmine and discretine. All these alkaloids are described for the first time in G. olivacea and their chemotaxonomic significance was discussed. The structure elucidation of these isolated alkaloids was established by extensive analyses of 1D and 2D NMR spectroscopy in combination with MS. The NMR data for atherosperminine, argentinine, and atherosperminine N-oxide were reviewed.