On various single crystal alkali halides, pentacene films were formed epitaxially by vacuum-deposition. On KCl and KBr the films show good epitaxy being composed of monomolecular layers with about 1.5 nm height. These films orient in two epitaxial angles with respect to the a-axis of the substrates. From the point-on-line epitaxy, the epitaxial orientations are almost successfully explained. As for the crystal structures, so-called thin-film phase was observed except for KI substrate. The unit cell dimensions are 1.54 nm d-spacing perpendicular to the substrates and its in-plane unit cell sizes of a=0.59 nm, b=0.75 nm and Gamma=90 degrees which are almost the same to the values reported previously on SiO2/Si. (c) 2005 Elsevier B.V. All rights reserved.