Epitaxial thin films of NiO(111) were successfully fabricated on α-Al2O3(0001) substrates at room temperature using a pulsed laser deposition method. The oxygen pressure and laser fluence dependences on the film quality, and the relationship between the in-plane lattice parameter and the crystallinity of NiO(111) epitaxial films were investigated. The room-temperature epitaxial growth of NiO(111) thin films on α-Al2O3(0001) substrates can be explained by a higher order epitaxy mechanism enabling the fourfold longer in-plane lattice parameters of NiO(111) to match the threefold longer parameters of α-Al2O 3(0001) with less than a 4.5% misfit. The expansion of the in-plane lattice parameter was caused by the excess oxygen in the epitaxial films, and improve the crystallinity of the films. The reflection high-energy electron diffraction (RHEED) observations for the epitaxial films with good crystallinity showed that the in-plane lattice parameter was extended by about 5% compared with that of the bulk with a film thickness of 1 nm or less. According to the higher order epitaxy mechanism, the improvement of the crystallinity is due to the relaxation of the lattice misfit between the substrate and the film with a film thickness of 1 nm or less.