The crystalline structure of mangiferin (¼ 2-b-d-glucopyranosyl-1,3,6,7-tetrahydroxy-9H-xanthen-9-one; 1), a biologically active xanthenone C-glycoside, isolated from the stem bark of Mangifera indica (Anacardiaceae), was unambiguously determined by single-crystal X-ray diffraction (XRD). The crystal structure is summarized as follows:, and Z ¼ 2. The structure also shows two molecules in the asymmetric unit cell and five crystallization H 2 O molecules. The packing is stabilized by several intermolecular H-bonds involving either the two symmetry-independent mangiferin molecules 1a and 1b, or the H 2 O ones.