A high-performance hydrogen gas sensor has been developed that utilizes a proton affinity of 1,4-diketo-3,6-bis-(4'-pyridyl)-pyrrolo-[3,4-c]-pyrrole (DPPP) known as a red pigment. We found that the N atom of the pyridyl ring of the DPPP can easily be protonated by protons dissociated from H-2 to induce a remarkable change in electrical conductivity by several orders of magnitude. The H-2 sensor operates in two steps: the first step is the dissociation of H-2 by means of a sputtered Pd-layer, followed by capturing protons by the N atom of the pyridyl ring (proton acceptor). The device structure is: electrode/Pd/DPPP/electrode. The appealing feature of the device is the reversible operation at room temperature as characterized by a change in electrical resistivity by two orders of magnitude even under 0.05% H-2. The material is quite stable and the device is simple and compact. © 2005 The Electrochemical Society. All rights reserved.