Turbulent lean premixed combustion plays a predominant role in reducing NOx emission due to the low flame temperatures. For turbulent premixed flames located in the thin-reaction-zones regime, small-scale eddies could penetrate into the preheat zone of the flames and enhance the mixing process. In this study, the effects of small-scale turbulence on NOx formation in premixed flame fronts are investigated through the incorporation of turbulence induced diffusion in the preheat zone of one-dimensional premixed flames for methane/air, simulated with the 53-species GRI-Mech 3.0 mechanism at both atmospheric pressure and engine conditions with different turbulence intensities. It is found that the NO generated in flame fronts deceases with increased intensity of small-scale turbulence and the effect is more pronounced at high pressures, where the turbulence-induced diffusion in the preheat zone can reduce the NOx formation in flame fronts by more than 40%. In addition, a flamelet-based approach that accounts for the flame thickening effects has been formulated to simulate NOx formation in turbulent lean premixed combustion. In this approach, the species NO is transported and solved in a simulation with its chemical source term modeled by combining its formation in flame fronts and its integrated formation rate in the post-flame zone from 1-D premixed flames with detailed chemical kinetics and turbulence induced diffusion. (C) 2013 Elsevier Ltd. All rights reserved.