Tanzawaic acids M (1), N (2), O (3) and P (4) and the known tanzawaic acids B (5) and E (6), have been isolated from an extract of a cultured marine-derived fungus (strain CF07370) identified as a member of the genus Penicillium. The structures of 1–4 were determined based on spectroscopic evidence. The antimicrobial and cytotoxic activities of compounds 1–6 were evaluated.