Extraction and chromatographic separation of the extracts of dried leaves of Glycosmis lucida lead to the isolation of a new acridone alkaloid lucidaine A (1), along with two known analogues 2 and 3. The structure of 1 was established by extensive spectroscopic analysis (1D and 2D NMR, HR-ESI-MS), and the known compounds were identified by comparisons with data reported in the literature. Furthermore, the cytotoxicity activities of all isolated alkaloids in vitro were evaluated.