A new polyamine-modified indole derivative protoaculeine B (1) was isolated from Okinawan marine sponge Axinyssa aculeata. The structure of 1 was assigned on the basis of spectral data along with chemical transformations. Because the structure of 1 greatly inferred the N-terminal amino acid for highly modified peptide toxin aculeines, the probable structure for aculeine B was proposed on the basis of high-resolution mass spectral analysis.