The epitaxial relationships of vapor-deposited thin films of pentacene on anthracene single crystal were investigated by X-ray diffractometry. The in-plane and out-of-plane structures of the thin films were investigated using a four-axis X-ray diffractometer. The thin-film phase of pentacene was confirmed in the deposited films, and the epitaxial relationship was determined. Uniaxial in-plane orientation was observed as well as the orientation of substrate normal direction. The mechanism of epitaxy is discussed in terms of lattice matching in [110] direction. (c) 2007 Elsevier B.V. All rights reserved.