The present invention relates to a metallic nanoparticle catalyst, and more particularly, to a porous catalyst in which metallic nanoparticles are embedded in a porous oxide support, and a method for preparing the porous catalyst. To this end, a porous catalyst composition having metallic nanoparticles of the present invention includes an oxide matrix structure having mesopores and micropores; and metal or metal oxide nanoparticles embedded in the oxide matrix structure having the mesopores and micropores. A method for preparing a porous catalyst composition having metallic nanoparticles of the present invention includes a step of covering metallic nanoparticles containing at least any one of a metal and a metal oxide with a stabilizer to stabilize the metallic nanoparticles and then binding a polymer to surfaces of the metallic nanoparticles to functionalize the metallic nanoparticles; a step of mixing an oxide precursor with a solution in which the functionalized metallic nanoparticles and an activator are mixed and dispersed, thereby synthesizing a metallic nanoparticle dispersion embedded in a porous oxide support; and a step of calcining the metallic nanoparticle dispersion. Thus, metallic nanoparticle catalysts having high activity even at low temperature are realized.