We report the results of comparative study of monolayer films of n-hexacontane (C60H122) adsorbed on atomically flat graphite and reconstructed Au(111) surfaces. Scanning tunneling microscopy (STM) revealed polymorphism in monolayer on Au(111) surface. It was shown that under the same conditions of deposition hexacontane molecules may form two packing structures. The effect of collective reorientation of molecules was revealed on graphite surface. Obtained results are explained in terms of commensurability between alkyl chain and substrate.