The characteristics of the experimental ejector in a steam refrigeration system were studied over a range of evaporator temperatures from 5 to 15°C, boiler temperatures from 95 to 135°C, and condenser pressures from 23.37 to 53.18 mbar (i.e., condenser temperatures from 20 to 34°C). It was shown that when increasing the boiler temperature, the entrainment ratio first increased and then decreased. Optimum boiler temperatures existed for each primary nozzle. The choking phenomena in secondary flow play an important role in ejector performance, causing the so-called “constant capacity” for the system. The entrainment ratio increased rapidly as evaporator temperature was raised, making it economical to run the system at high evaporator temperatures. Furthermore, an ejector performance map was derived from the experimental data for analyzing the optimum operation control of the system.