A near-azeotropic refrigerant mixture named BY-4 was developed for a high temperature heat pump in the paper. The study tested the experimental performance of single-stage high temperature heat pump with BY-4 as work fluid. Under the experimental conditions of the inlet water temperature of evaporator at 50-70 degrees C, the outlet water temperature of condenser could reach 80-110 degrees C. The maximum pressure of the system was only 1.73 MPa even when the output temperature rose up to 110 degrees C. The experimental results showed that the COP (coefficient of performance) of heat pump was higher than 3.5 when the temperature difference between the condenser outlet water and the evaporator inlet water was less than 30 degrees C. Thus, BY-4 was recommended as working fluid for high temperature heat pump with a single-stage cycle due to its good comprehensive properties and excellent cycle performance. (C) 2014 Elsevier B.V. All rights reserved.