<jats:title>Abstract</jats:title><jats:p>Two new indole alkaloids, arsindolines A and B (<jats:bold>1</jats:bold> and <jats:bold>2</jats:bold>, resp.), together with six known indole alkaloids, were isolated from a marine‐derived bacterium strain CB101, identified as <jats:italic>Aeromonas</jats:italic> sp. Their structures were established by spectroscopic methods, and their antitumor activities were evaluated by SRB and MTT methods.