Chemical investigation of the EtOH extract from the tubers of Stephania succifem collected in Hainan Province of China resulted in the isolation of the two new alkaloids Cepharanone D (1) and N-formyl-asimilobine (2), and a known alkaloid, N-formyl-annonain (3). Their structures were elucidated by spectroscopic techniques (UV, IR, ID and 2D NMR). The antimicrobial activities of the three compounds were also investigated.