Natural products have long been an important source for the discovery of biologically active compounds, in particular, drug leads. Delavatine A (1), a structurally unusual cyclopenta[de]isoquinoline alkaloid, was isolated from Incarvillea delavayi. Extensive spectroscopic analysis, in combination with biogenetic speculation, established the structure of 1. Delavatine A (1) exhibited considerable cytotoxicity against a number of cancer cell lines with IC₅₀ values in the range of 4.28 to 6.61 μg mL⁻¹.