Copper(II) oxide (CuO) nanoparticles have been synthesized from copper acetate by simple precipitation method and were found to be an efficient and inexpensive catalyst for C-N cross-coupling reactions of benzimidazole with various aryl halides. The catalyst was characterized by scanning electron microscope, transmission electron microscope, Brunauer-Emmett-Teller-surface area, and X-ray diffraction analysis. Benzimidazole undergoes reaction with aryl bromides, aryl chlorides, or aryl fluorides in the presence of K2CO3 at moderate temperature. The yield of N-arylated benzimidazole is ranging from 55 to 92%. The effect of the particle size of the catalyst on N-arylation of benzimidazole with 4-chlorobenzonitrile was studied. Reusability of the CuO nanoparticles was also carried out, and the results were found to be good.