The crystal structure of the L-sorbose dehydrogenase (SDH) from Ketogulonicigenium vulgare Y25 has been determined at 2.7 Å resolution using the molecular replacement method. The overall structure of SDH is similar to that of other quinoprotein dehydrogenases; consisting of an eight bladed β-propeller PQQ domain and protrusion loops. We identified a stable homodimer in crystal and demonstrated its existence in solution by sedimentation velocity measurement. By biochemical characterization of the SDH in vitro, using L-sorbose as substrate and cytochrome c551 as electron acceptor, we revealed cytochrome c551 acting as physiological primary electron acceptor for SDH.