The present work focused on the chemical study of the main alkaloid component in Brazilian indigenous Amaryllidaceae species Hippeastrum puniceum (Lam.) Kuntze. The strategy applied was based on a distinct partitioning process and chromatographic-purification steps using the crude methanolic extract as the starting material. In this way, the glycosylated derivative narciclasine-4-O-β-D-xylopyranoside was isolated from the ethyl acetate fraction of H. puniceum. Structural elucidation of the compound was performed through NMR (Nuclear Magnetic Resonance) analysis including mono- and bi-dimensional experiments. The absolute configuration was determined herein for the first time by means of X-Ray Crystallography. The compound was also evaluated as cytotoxic agent against colon (HCT 116) and breast (MCF-7) tumor cells, showing no significant activity at the tested concentrations of 10 and 50 μM. © 2020 SAAB