Irreversibility analyses of R290, R717, R718 and R744 are carried out in a compression refrigeration cycle. The effects of evaporator temperature, condenser temperature and isentropic efficiency on the irreversibility of the cycle and its basic components are investigated and exergy analysis of the cycle is also presented as a function of evaporator and condenser temperatures. The irreversibilities of the natural refrigerants decrease as the evaporator temperature and isentropic efficiency increase, whereas those increase with the increasing values of condenser temperatures. The highest irreversibilities generally occur in the condenser, and the lowest ones occur in the evaporator.