Reactions of poly(vinylidene fluoride) [PVDF], poly(vinylidene fluoride-co-hexafluoropropylene) [poly(VDF-co-HFP)] copolymer, and poly(vinylidene fluoride-co-perfluoromethyl vinyl ether) [poly(VDF-co-PMVE)] copolymer in subcritical water were performed with the aim to develop a technique for recycling fluorine element. By addition of KMnO4 to the system, quasi-complete mineralization of PVDF was achieved at a rather low temperature (250 degrees C). When PVDF was reacted for 18 h in the presence of KMnO4 (158 mM, corresponding to a 1.6-fold molar excess relative to both fluorine and carbon atom contents of PVDF), the fluoride ions (F) yield reached 100%, and the amount of remaining total organic carbon decreased to 2% of the carbon atoms in the initial PVDF. Poly(VDF-co-HFP) and poly(VDF-co-HFP) copolymers also showed quasi-complete mineralizations under the same conditions. During the reactions, MnO4- was modified into MnO2. Compared to the previous method using H2O2, the reaction temperature that allows a complete mineralization was reduced by 50 degrees C.