Introduction: We examined the thermophysiological effects of ultrafine bubble (UB) bathing in comparison with microbubble (MB) and freshwater (FW) bathing.   Subjects and Methods: Seven healthy women aged 35.6±2.9 years provided informed consent to participate in the study. After a 10-min rest, each subject engaged in UB, MB, and FW bathing (on separate days) at 40°C for 10 min. During the experiment, tympanic temperature, local sweat rate, local skin temperature, heat flow, and heart rate variability were continuously recorded. Subjective assessments of thermal sensation and comfort were rated on a visual analog scale between 0 to 100.  Results: Increases in tympanic temperature and mean body temperature were highest during MB bathing, and similar increases were observed during UB and FW bathing. Local sweating was highest during MB bathing and lowest during UB bathing. A significant interaction was observed between local sweating during bathing and bathing style (P<0.001). The increase in local sweat rate relative to body temperature was lowest during UB bathing and highest during MB bathing.  Discussion: During UB bathing, UBs and MBs that were generated in high concentrations in the bathtub decreased the flow of heat to the body, thereby suppressing an increase in tympanic temperature and yielding the lowest local sweat late. However, during MB bathing, in which a moderate concentration of UBs and MBs were generated, the increase in heat flow due to the convection of hot water exceeded the decrease in heat flow due to the bubbles.  Conclusions: The results suggest that bubble properties and convection characteristics altered the balance of heat flow, leading to differences in the thermoregulatory response during and after bathing.