The effects of turbulence on momentum, heat, and mass transfer during laser welding of a copper-nickel dissimilar couple are studied by carrying out three-dimensional unsteady Reynolds Averaged Navier Stokes (RANS) simulations. The turbulent transport is modelled by a suitably modified high Reynolds number k-epsilon model. The solid-liquid phase change is accounted for by a modified enthalpy porosity technique. In order to demonstrate the effects of turbulence, two sets of simulations are carried out for the same set of processing parameters: one with the turbulence model, and the other without activating the turbulence model. The enhanced diffusive transport associated with turbulence is shown to decrease the maximum values of temperature, velocity magnitude, and copper mass fraction in the molten pool. The effects of turbulence are found to be most prominent on the species transport in the molten pool. The composition distribution in turbulent simulation is found to be more uniform than that obtained in the simulation without turbulent transport. The nickel composition distribution predictions, as obtained from the present turbulence model based simulations, are also found to be in good agreement with the corresponding experimental results. (c) 2006 Elsevier Ltd. All rights reserved.