The newly developed concept of MILD combustion has paved the way through achievement of high thermal efficiencies with low levels of pollutants and greenhouse gases. High fidelity numerical models play key role in design and optimization of these burners. The present research aims to assess the effect of molecular diffusion and deviations in the amount of different species Schmidt number on the precision of the model. To this end, a previously investigated MILD burner is opted as case-study. From the results it is evident that in contrast to conventional combustion regimes problems, the impact of the often-neglected laminar diffusion is comparable to turbulent diffusion. On the other hand, consideration of molecular diffusion in the species transport equation significantly improves the model accuracy only if proper Schmidt number for species are considered. Suitable Sutherland coefficients and Schmidt numbers for each species are found based on relevant data in the literature and reported.