Abstract: A process for converting Compressed Natural Gas (CNG) to Liquefied Natural Gas (LNG) is modelled thermodynamically and effects of design and operating parameters on exergy destruction and performance of the process are studied. Results show that CNG pressure, pressure after Joule–Thomson valve, and temperature of CNG after heat exchanger of refrigerating system have significant effects on optimum design and operation of the process. The results also indicate that the effects of CNG temperature after CNG production section, and pinch temperature of the last heat exchanger of the process are considerable. To determine the effects of natural gas composition on operating the CNG to LNG converting (CLC) process, variation of nitrogen as the most effective content of natural gas on operating the process has been studied and discussed.