Magnetization curves of MnBi thin films have been measured in the temperature range between room temperature and 77°K. Films were prepared on glass substrates with a protection layer of SiO2by vacuum deposition. There occurs a large thermal hysteresis of the magnetization curves, which has not been known of bulk specimens. The magnetic domain configuration at 77°K and the dependence of magnetic anisotropy energy on temperature were also studied. The thermal hysteresis is due to some relaxation mechanism. It is suggested that a thermomagnetic writing other than the Curie‐point writing will be possible, if the thermal hysteretic property is made use of.