In presentwork, a sub-coolingauxiliary system is integrated with vapour compression refrigeration system to predict the performance characteristics and energy saving of the system. An experimental investigation was performed to determine the performance parameters at various operating conditions using two types of refrigerants, R-134a and zeotropic mixed refrigerant R-404A.Investigating the results hasshowed that, the enhancement in performance of the refrigeration system with sub-cooling circuit compared with that for system without sub-cooling for R-134a was about 5% increase in RE, 14% optimization in COPand 2.8% energy saving for different thermal loads applied on the evaporator.While for R-404A, the increase in RE was 4%, the optimization in COP was about 13% and 3.7%energy saving. There is a significant improvement in the performance of the system with R-404A compared with that forR-134a at the same operating conditions.