Marine tunicates have proven to be a rich source of intriguing structures and interesting biological activities. In our continuing survey of bioactive compounds from Okinawan marine organisms, we have reported a novel β-carboline, named eudistomidin A (1), with powerful calmodulin antagonistic activity from the Okinawan tunicate Eudistoma glaucus. This paper describes the isolation and structure elucidation of eudistomidins B (2), C (3), and D (4), three new pharmacologically active components from this tunicate. The configuration at C-10 of eudistomidin C (3) was established by synthesis of 10-(R)-O-methyleudistomidin C. This tunicate also contained four known compounds, eudistomins D (5), E (6), H (7), and I (8), previously isolated from the Caribbean tunicate Eudistoma oliuaceum.