Carbon-encapsulated copper nanoparticles (CECNPs) are synthesized from a precursor derived easily through a refluxing method. The as-synthesized CECNPs are monodispersed with a uniform size distribution and obvious core-shell structure. The formation process of the CECNPs is investigated, and the possible mechanism is proposed. Furthermore, TG-DSC measurements, in conjunction with the corresponding XRD patterns, reveal that the as-synthesized CECNPs show excellent oxidation resistance to temperatures up to 900 degrees C.