Anodic polarization measurements for various ruthenium (Ru) alloys revealed that hexagonal close-packed nanoporous Ru (np-Ru) can be fabricated by dealloying or selective dissolution of manganese (Mn) from Ru–Mn alloy. The pore size and specific surface area of fabricated np-Ru were 3 nm and 51.5 m² g⁻¹, respectively. An electron diffraction pattern suggested a polycrystalline nature of the fabricated np-Ru, which is perhaps due to the change in the crystal structure during dealloying. The oxidation of carbon monoxide (CO) was efficiently catalyzed by the np-Ru. The activation energy was 82 kJ mol⁻¹ which is comparable to that of the polycrystalline RuO₂/Ru catalyst. The present np-Ru is a novel candidate as a recoverable Ru catalyst.