Chemical investigation of the sponge Leucetta chagosensis collected in Indonesia afforded five new imidazole alkaloids, naamine F (2), naamine G (3), kealiinine A (6), kealiinine B (7), and kealiinine C (8), in addition to the known compound naamine A (1). Naamine G (3) exhibited strong antifungal activity against the phytopathogenic fungus Cladosporium herbarum and also showed mild cytotoxicity against mouse lymphoma (L5178Y) and human cervix carcinoma (HeLa) cell lines. In the brine shrimp assay, kealiinine A (6) was more active than naamine G (3). The structures of the new compounds were unambiguously established by 1D and 2D NMR and MS data.