Abstract: The effective emissivity of the blackbody cavity is a key characteristic of the blackbody radiation source for ear thermometer calibration and verification. The emissivity characteristics of the blackbody cavity recommended by the ear thermometer calibration protocol are presented, and brightness temperature comparison experiments are conducted with the blackbody cavities of two international standards recommended for ear thermometers. Based on the data analysis, an evaluation of the three ear thermometer blackbody cavities is given.