A new acridone alkaloid, melixyloidin (1), and two known alkaloids (2-3) were isolated from Melicope xanthoxyloides (F. Muell) T.G. Hartley leaves. The structure of melixyloidin were elucidated using NMR spectra and high-resolution ESIMS data. Acridone alkaloids 1-3 were evaluated against MCF-7 and HeLa cells. 1,3,4-Trimethoxy-10-methylacridin-9-one (2) showed potent cytotoxic activity against MCF-7 cells with an IC50 value of 5.31 mu M.