Pt/C–RuO2·xH2O catalyst was successfully prepared through the deposition of hydrated RuO2·xH2O on Pt/C catalyst for a proton exchange membrane fuel cell (PEMFC). The Pt/C and Pt/C–RuO2·xH2O catalysts were compared using physical and electrochemical techniques. The ON–OFF cycling test results showed sudden cell failures after 1,850 and 1,160 cycles for Pt/C–RuO2·xH2O and Pt/C, respectively. Nearly 11.2% of the cell voltage of Pt/C–RuO2·xH2O was lost after 1,160 cycles, compared with 26.3% for Pt/C. The charge transfer resistances of Pt/C–RuO2·xH2O and Pt/C increased from 0.5217 and 0.5366 Ω to 0.5732 and 0.7261 Ω, respectively. The remaining electrochemical active surface area of Pt was about 30.6% in Pt/C and about 68.9% in Pt/C–RuO2·xH2O after the ON–OFF test. The mean particle size of Pt/C significantly increased from 4.6 to 8.9 nm, whereas that of Pt/C–RuO2·xH2O increased from 4.3 to 6.3 nm. Therefore, the long-term durability of Pt/C–RuO2·xH2O in a PEMFC was much better than that of Pt/C.