This paper proposes a modified vapor-compression refrigeration cycle (MVRC) system operating with the zeotropic mixture R290/R600a for domestic refrigerator-freezers. In the MVRC system, a phase separator is introduced to enhance the overall system performance. A theoretical energy and exergy analysis on the performance of the MVRC is carried out by using the developed mathematical model, and then compared with that of the traditional vapor-compression refrigeration cycle (TVRC) operating with the refrigerant R600a and the zeotropic mixture R290/R600a, respectively. According to the simulation results of these two cycles, the MVRC can give the most excellent performances in the COP (coefficient of performance), the volumetric refrigeration capacity, the total exergy destruction and the exergetic efficiency under the same given operating conditions. Therefore, the performance characteristics of the MVRC may show its promise in domestic refrigerator-freezer applications.