Sample of Ho x Er 1−x N (x=0.25, 0.5, 0.75) were synthesized by hot isostatic pressing of alloy blocks in nitrogen gas and their specific heat were measured under zero-field and 5T. The peak value of the specific heat associated with the ferro–para magnetic transition of Ho x Er 1−x N was lager than that of Er 3 Ni which is used commercially as a magnetic regenerator for the Gifford–McMahon refrigerator. Magnetic entropy change ΔS and adiabatic temperature range ΔT were evaluated from entropy curves under zero-field and 5T. Both the properties were very promising from viewpoints of application of rare-earth mononitride to the magnetic refrigerant and/or regenerator working at cryogenic temperatures around their Curie's temperature.