Effects of the stuffiness of medical X-ray protective clothing on human physiology and subjective feeling should be addressed. Therefore, we developed novel protective clothing with a moisture-permeable function in our previous report. In this study, we examined the effects of the newly developed protective clothing on thermal performance and human physiology. The subjects included thirteen females in their 20s. The following parameters were experimentally measured and evaluated: temperature and humidity within the protective clothing (Tcl and Hcl), skin temperature (Tsk), sweating rate (Sw), tympanic temperature (Tty), heart rate (HR), and subjective feeling. Consequently, both Tcl and Tsk in the developed protective clothing were lower than those of the existing clothing. Additionally, when the novel protective clothing was worn, Sw and HR were significantly lower than those of the existing protective clothing. A subjective evaluation of the novel protective clothing verified that it was neither hot nor stuffy. This indicates the possibility that the novel protective clothing reduces the physiological and psychological load. Furthermore, it was indicated that the influences on the temperature and humidity within the protective clothing and the physiological load were low even when the waist belt was fastened.