Size effects on both equilibrium and kinetic surface segregations in Ni-Cu alloy thin films are simulated based on the modified Darken model for a finite sized film system. The simulations are carried out for all compositional ranges and film thicknesses. The segregation energy used for the simulation is taken from that of the corresponding Ni-Cu bulk material, which could be obtained by fitting the experimental data and/or calculated according to the Miedema model. The size effect on segregation depends on segregation energy, initial bulk concentration, temperature and film thickness. (C) 2012 Elsevier B.V. All rights reserved.