A new azaoxoaporphine alkaloid, 8,9-dimethoxysampangine (1), and a new naphthyridine alkaloid, 7-methoxy-8-hydroxyeupolauridine (2), along with two known azaoxoaporphine alkaloids, sampangine (3) and 9-methoxysampangine (4), were isolated from the EtOAc extract of the barks of Polyalthia nemoralis. Their structures were established on the basis of spectral evidences. Compound 1 exhibited significant cytotoxicity against KB, MCF7, LU-1, HepG2, LNCap, SW626 and SW480 cancer cell lines with IC50 values in the range of 5.06.,b0.04-7.61.,b0.06 μM.