The crystal structure of the l-sorbose dehydrogenase (SDH) from Ketogulonicigenium vulgare Y25 has been determined at 2.7 resolution using the molecular replacement method. The overall structure of SDH is similar to that of other quinoprotein dehydrogenases; consisting of an eight bladed beta-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.