Hexarates are platform chemicals. Methods to produce D-glucarate and D-mannarate are desirable because these hexarates can be gained by oxidation of the corresponding hexuronates, which are abundantly found in algae and plants as the units of polyuronates. Oxidative production of the hexarates can be combined with a reductive reaction to coproduce electricity. An enzymatic biofuel cell is a device that enables this coproduction. To construct the cell, it is necessary to find enzymes that catalyze platform chemical production and are also suitable as anode catalysts. Here, we show the production of D-glucarate and D-mannarate from D-glucuronate and D-mannuronate, with both reactions catalyzed by pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase, in addition to the production of D-glucarate from L-guluronate by the PQQ domain of pyranose dehydrogenase from Coprinopsis cinerea. The enzymes are suitable as anode catalysts in biofuel cells that coproduce these hexarates and electricity.