Manzamine alkdloids are well known to be a group of marine natural products, which have a β-carboline moiety and a unique heterocyclic ring system. Since manzamine A had been isolated from a marine sponge Haliclona sp. in 1986, approximately 100 manzamine alkdloids containing biogenetic precursors have been idolated so far. A great number of studies on them, such as isolation and structural analysis, biosynthesis, and total synthesis, have been actively performed due to their intriguing structures and intersting biological activities. We have also isolated s seris of manzamine alkaloids from several genera and their structures have been elucidated by means of NMR spectra, chemical correlations, X-ray crystallography, and CD spectra. During our continuous search for structurally interesting metabolites from marine sponges, new manzamine alkdloids, zamamidines A-C (1-3), have been isolated, and their structures were elucidated by spectroscopic data. 1-3 are new manzamine alkdloids possessing a second β-carboline ring via an ethylene chain at N-2 of manzamine H, 1,2,3,4-tetrahydromanzamine B, and manzamine D, respectively. Since no manzamine alkdloids possessing any side chain at N-2 other than a methyl group have been reported to date, 1〜3 are the first examples of it. Zamamidines A-C (1-3) showed inhibitory activities against Plasmodium falciparum (Kl strain) and Tripanosoma brucei brucei (GUTat 3.1) in vitro.