Abstract: Since long time, it has been noticed that refrigerators are the devices which work almost 365 days round the clock; hence objective of energy efficiency improvement attracts much. There are several ways of improving the performance of a vapor compression refrigeration cycle. Use of an ejector as expansion device is one of the alternative way. The advent of new component ‘Ejector’ into refrigeration system opened the new era of research. The vital component, which decides the effective operation of the ejector expansion refrigeration system, is the ejector. Hence, design of an ejector and analyses of its physical and operational parameters have drawn special attention. The thermodynamic analysis of natural refrigerant (R 170) based vapour compression refrigeration cycles is presented in this article using a constant pressure mixing ejector as an expansion device. Using ejector as an expansion device, R 170 yields a maximum COP improvement of 24.12 percent.