Two new acridone alkaloids, margrapine-A and -B were isolated from the roots of Marsh grapefruit (Cirrus paradisi Macf.). Their structures were characterized on the basis of spectroscopic evidence. In the course of our research on the phytochemical aspects of Citrus plants, we have demonstrated the isolation and structure elucidation of many new acridone alkaloids and coumarins. Previous investigation of the constituents of the roots of Marsh grapefruit (C. paradisi Macf.) furnished to isolate new acridone alkaloids, azacridone-A, citbismine-B,-C,-D,-E, furoparadine, trans-dihydrocitracridone-I, marshdine and marshmine. Further investigation resulted in the isolation of two new acridone alkaloids, named margrapine-A (1) and -B (2). In this paper, we wish to report the structural elucidation of these new alkaloids.