Nano-powder of R-type manganese dioxide (RMO) was used for a hydrogen gas sensor. We prepared a pellet (diameter: 2 cm, thickness: 0.5 mm) of RMO, and set it in between a couple of Pt mesh sheets to make a SOFC cell. The cell showed a maximum output voltage of 0.3 V with good response to hydrogen gas supplied at room temperature. We measured the variation of the output voltage by using different concentration of hydrogen gas (0.1- 99.9 %) and their flow rate (10- 100 ml/min). Furthermore, other crystal structure types of manganese dioxide were tested for comparison. Consequently, only RMO showed good suitability as a hydrogen gas sensor, usable over a wide range of hydrogen gas concentrations. ©The Electrochemical Society.