In this paper, we discuss the influence of the electron mean free path on resistivity of thin metal films. The simulation results obtained by using Fuchs-Sondheimer's and Mayadas-Shatzkes's models indicate that metals with a smaller electron mean free path exhibit the size effect for smaller dimensions. This point is supported by the electrical measurements on aluminium and copper thin films, which are compared in terms of the corresponding grain boundary reflection coefficients. The resistivity of silver films increases abruptly as film thickness is below the electron mean free path, resulting in difficulty in extracting the grain boundary reflection coefficient. Hence it is difficult to separate the influence of electron mean free path from other factors by comparing silver with aluminium or copper. However, the normally observed strong increase in resistivity with decreasing film thickness in pure metals is absent in ordered CuAu I thin films, which confirms the previous conclusion. (C) 2004 Elsevier B.V.. All rights reserved.