New ceriporic acids—alkadienyl and alkenyl itaconic acids having a bis-allyl (3-[(Z,Z)-hexadec-7,10-dienyl]-itaconic acid; ceriporic acid G) and a monoene (3-[(Z)-octadec-9-enyl]-itaconic acid; ceriporic acid H) structure in their side chains—were isolated from the cultures of the selective lignin-degrading fungus Ceriporiopsis subvermispora. The new metabolites ceriporic acid G and H were synthesized by a cross-aldol condensation and a Grignard substitution reaction, respectively. Ceriporic acid G triggered the manganese peroxidase (MnP)-catalyzed lipid peroxidation and decomposed a recalcitrant non-phenolic lignin substructure model compound. Except for simple fatty acids, this is the first report of a fungal metabolite that induced ligninolytic lipid peroxidation.