In this paper, the cycle performance characteristics of a cascade refrigeration system with internal heat exchanger using natural refrigerants is presented to offer the basic design data for the operating parameters of the system. This system considered in this study is consisted of a high temperature cycle using a carbon dioxide(R744) and low temperature cycle using refrigerants such as R290, R1270, R600a and Ethane. The main results were summarized as follows : The COP of the cascade refrigeration system of R600a with internal heat exchanger is the highest grade in low temperature cycle using refrigerants such as R290, R1270, R600a and Ethane. The COP of the cascade refrigeration system with internal heat exchanger only in high temperature cycle is the highest value among three type cycle, such as only low temperature cycle, only high temperature cycle and all the cycle.