Two new sesquiterpene hydroquinones, polyfibrospongols A (1) and B (2), were isolated from the Taiwanese marine sponge Polyfibrospongia australis Lendenfeld (Spongiidae) in addition to the known metabolites, dictyoceratin A (3), ilimaquinone (4), and 5-epi-ilimaquinone (9). The structures of these compounds have been determined mainly on the basis of spectral and chemical methods. Biological testing revealed that compounds 1 and 2 exhibited significant cytotoxicity against human KB-16, A-549, and murine P-388 tumor cell lines.