Abstract： Objective To study the chemcial constituents in mangrove plant, Xylocarpus granatum. Methods The constituents were isolated through chromatography, and the structures were elucidated by spectroscopic methods. Results One maxicanolide-type limonoid, named xylogranatin S, was isolated from the 95% ethanol extract of X. Granatum and the inhibitory activities of the compound on HeLa, HLE, MDA-MB-231, and SW-620 cells were studied by MTT method. Conclusion Xy|ogranatin S is a new compound and shows no significant inhibitory effect on the above cells.