The performance of a refrigeration cycle with carbon dioxide was experimentally investigated. The effects of mass flow rate of carbon dioxide, higher side pressure and refrigerant mass on the cooling coefficient of performance, cooling capacity and compressor work were examined. Then cooling coefficient of performance decreased and cooling capacity increased with an increase in mass flow rate of carbon dioxide. The cooling coefficient of performance had maximum value at a gas cooler outlet pressure of around 8.3 MPa regardless of compressor speed. A higher cooling coefficient of performance will be obtained by controlling gas cooler outlet pressure. Furthermore, compressor work increased with an increase in gas cooler outlet pressure regardless of refrigerant mass. The cooling coefficient of performance and cooling capacity increased with an increase in refrigerant mass.