For nano-scale thin film, effects of surface and interface, which can be ignored on a macroscale, become important. For example, surface energy and surface stress are key parameters for predicting the intrinsic stress of thin films. Several researchers have reported that the elastic constants of thin films are different from those of bulks. We have recently proposed new definitions and calculation methods regarding 14 surface stress and elastic constants for thin films by extending Martin's method, which is useful for obtaining internal displacement and elastic constants within the framework of the molecular dynamics (MD) method. We applied our method to nano-scale thin films of crystal and amorphous silicon. It is found that elastic constants of thin film depend on both the surface elastic constants and on film thickness. Those values are significantly affected by the surface reconstructions. The width of the surface and the limit of continuum homogeneous approximation are also investigated. (C) 2004 Elsevier B.V. All rights reserved.