In this paper, a transcritical ejector refrigeration cycle (TERC) using refrigerant R143a as working fluid is proposed to improve the performance of the ejector refrigeration systems driven by low-grade thermal energy. This method adopts an adequate combination of thermal and mechanical energy through the operation of the transcritical process for generator to enhance the performance of the conventional ejector refrigeration cycle (ERC) at the cost of additional driving mechanical energy. The performance characteristics of the TERC are investigated based on theoretical simulations. The TERC is also compared with the conventional ERC using refrigerant R134a. The study shows that when utilizing the low-grade thermal energy, the TERC yields significant increase in COP by adding auxiliary mechanical energy of the cycle pump and has a higher potential in making effective use of the low-grade thermal energy with gradient temperature, such as solar energy gained by a flat plate or evacuated tube solar collector. This also indicates that the TERC is an attractive alternative to the ejector refrigeration systems driven by low-grade thermal energy. Further experimental work for the TERC may be launched in the near future to verify practical applications. (C) 2010 Elsevier Ltd. All rights reserved.