The safe application of H-2 gas requires a high-performance H-2 gas sensing system. An attractive H-2 gas sensor for industrial application which has H-2 gas selectivity, high sensitivity, high response, high durability, small size, and low cost has not been developed yet. Durability is one of the most important problems in H-2 gas sensors using Pd. This study focused on electric resistivity changes in metallic Pd with hydrogen gas absorption. Nanostructured palladium (NSPd) films for a hydrogen gas sensing material were fabricated by a dealloying method using dilute citric acid. Fabricated NSPd films exhibited a nanoscaled network structure or aggregated particle structure, a linear electric resistance change with hydrogen gas concentration, and high sensitivity compared to flat pure Pd films. Therefore, NSPd film is useful for hydrogen gas sensing applications and has both high sensitivity and low usage of the noble metal. Furthermore, we also revealed a degradation mechanism of pure Pd film due to repeated H-2 gas exposure, and this phenomenon did not appear in the NSPd film. NSPd also showed a higher durability with repeated H-2 gas exposure compared to pure Pd film. We concluded that NSPd is suitable for use as a practical H-2 gas sensor due to its cost effectiveness and high sensing ability.