Much attention has been devoted to efforts to operate polymer electrolyte fuel cells (PEFCs) at temperatures above 100°C in order to avoid the problem of serious CO poisoning of the anode catalyst. It is also of great concern to operate PEFCs under low-humidity conditions, because the space and energy required for external humidification are eliminated or minimized in the fuel cell system. Thus, proton-conducting materials that can satisfy the above criteria have been proposed, developed, and evaluated worldwide. In particular, recent research efforts have been increasingly focusing on the design of anhydrous proton conductors, since these materials, at least in principle, do not need the presence of water as a charge carrier. We have recently found that In, Al, or Mg-doped SnP₂O₇ show high proton conductivities>10⁻¹ S·cm⁻¹ between 150 and 350°C under water-free conditions. Attempts to apply these materials as electrolytes in some electrochemical devices were also made. This paper presents an overview of the current status of doped SnP₂O₇ with principal emphasis on the materials aspect. In addition, the benefits of intermediate-temperature fuel cells using these materials are briefly summarized in terms of cell design, electrolyte and electrode materials.