The title compound, a natural b,d-seco-limonoid, C(27)H(34)O(8)·H(2)O, and known as Swietenolide monohydrate, has been isolated from S. macrophylla King. In the molecular structure, the four fused six-membered rings adopt twist-boat (ring A), approximate chair (ring B), envelope (ring C) and half-chair (ring D) conformations. The attached furan ring is essentially planar. O-H⋯O hydrogen bonds and weak C-H⋯O inter-actions connect the mol-ecules into a two-dimensional network parallel to the (100) plane. C-H⋯π inter-actions are also observed.