Nowadays the environment regulations have made the engine manufacturers to reduce emissions emitted from the engines. NOX is one of the most harmful pollutants in exhaust gases. By use of EGR (Exhaust Gas Recirculation), NOX could be reduced and controlled. Exhaust gas recirculation has proven to reduce nitrogen oxides (NOX) and smoke emissions simultaneously at relatively low cost compared to other reduction strategies. In this project we have used the variable valve timing to control the mass fraction of internal EGR in order to reduce NOX concentration in exhaust gases. To reach this goal, first the effect of RG (Residual Gas) on NOX formation has studied and then an exhaust valve lift profile is designed to reach optimized RG mass fraction.