Cast and vacuum-deposited films of several kinds of n-alkanes with different crystal systems were made on a glass substrate. X-ray diffraction (XRD) data showed that n-alkane molecules in both the cast and the vacuum-deposited films were essentially aligned perpendicularly on the substrate. When the vacuum-deposited film of n-alkane became thicker, the XRD pattern indicated that n-alkane molecules in the upper layer lay on the perpendicularly aligned n-alkane layer. Molecular alignment of the film of head-to-tail-type poly(3-hexylthiophene-2, 5-diyl), HT-P3HexTh, also depended on the thickness of the film.