An ejector is a machine for mixing and transporting fluid under vacuum. Ejectors enhance system efficiency, are easily operated, have a mechanically simple structure, and do not require a power supply. Because of these advantages, ejectors have been used in a variety of industrial fields such as refrigeration systems, power plants, and oil plants. In this work, an ejector was used to safely recycle anode tail gas in a 75 kW molten carbonate fuel cell (MCFC) system at Korea Electric Power Research Institute. In this system, the ejector was placed at the mixing point between the anode tail gas and either the cathode tail gas or fresh air. Because commercial ejectors are not designed for the operating conditions of our fuel cell system, a new ejector was designed for use beyond the operating limits of conventional ejectors. In this study, the entrainment ratio and anode outlet pressure were measured according to the ratio of the nozzle diameter to the throat diameter in the newly designed ejector. These results help to define important criteria of ejectors for MCFC recycling.