The formation of thin copper oxide (CuO) films on MgO(100) was studied by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The CuO films were grown by molecular beam epitaxy using NO2 as oxidant. For coverages exceeding 3 nm, the RHEED patterns indicate a two-dimensional growth of the CuO films with CuO(111) planes parallel to MgO(100). The in-plane epitaxial relationship is deduced as CuO[(1) over bar 10]parallel to MgO[011], The real space AFM images show that the CuO films exhibit a grain morphology with an average lateral dimension of the order of 200 nm. For CuO coverages above 5 nm, the secondary grains show a pronounced growth.