A new quinolinone alkaloid, Melicodenine I (1), along with five known compounds, bergapten (2), isoevodionol methyl ether (3), isoevodionol (4), ternatin (5), -sitosteryl-3-O--D-glucopyranoside (6) and a mixture of -sitosterol and stigmasterol were isolated from Melicope denhamii leaves, and their structures were elucidated using H-1 NMR, C-13 NMR, 2D NMR and UPLC-qToF-MS.