Two new alkaloids, hyrtimomines D (1) and E (2), were isolated from an Okinawan marine sponge Hyrtios sp. The structures of 1 and 2 were elucidated on the basis of spectroscopic analysis. Hyrtimomines D (1) and E (2) are structurally unique bisindole alkaloids possessing the canthin-6-one skeleton with a hydroxyindole and an imidazolium units. Hyrtimomines D (1) and E (2) exhibited antimicrobial activity. © 2013 Elsevier Ltd. All rights reserved.