Pandanus amaryllifolius Roxb. (Pandanaceae) is used as a flavor and in folk medicine in Southeast Asia. The ethanolic crude extract of the aerial parts of P. amaryllifolius exhibited antioxidant, antibiofilm, and anti-inflammatory activities in previous studies. In the current investigation, the purification of the ethanolic extract yielded nine new compounds, including N-acetylnorpandamarilactonines A (1) and B (2); pandalizines A (3) and B (4); pandanmenyamine (5); pandamarilactones 2 (6) and 3 (7), and 5(E)-pandamarilactonine-32 (8); and pandalactonine (9). The isolated alkaloids, with either a γ-alkylidene-α,β-unsaturated-γ-lactone or γ-alkylidene-α,β-unsaturated-γ-lactam system, can be classified into five skeletons including norpandamarilactonine, indolizinone, pandanamine, pandamarilactone, and pandamarilactonine. A plausible biosynthetic route toward 1-5, 7, and 9 is proposed.