A hybrid catalyst consisting of polymer-coated Ru nanoparticles (Ru-PVP, PVP: poly(N-vinyl-2-pyrrolidone)) embedded in a porous metal-organic framework of ZIF-8 (Ru-PVP@ZIF-8) was synthesized by the crystallization of ZIF-8 in a methanol solution of Ru-PVP. The structural properties of Ru-PVP@ZIF-8 were examined by N-2 gas adsorption, infrared spectra, and X-ray powder diffraction measurements. We successfully identified the most appropriate pretreatment conditions for surface activation of the Ru nanoparticles in the catalyst. The pretreated Ru-PVP@ZIF-8 was applied for a CO oxidation reaction with H-2 gas feeds. Ru-PVP@ZIF-8 was found to exhibit higher catalytic activities and higher CO2 selectivity than those observed on a carbon-supported Ru-PVP (Ru-PVP/C), implying that the pores of the ZIF-8 provide a more suitable environment for the reaction with O-2 and CO gases.