This research aims to use the outdoor thermal environment evaluation index ETFe to quantify effects on the thermal sense of the human body of a tropical region climate with small annual temperature differences, and to examine seasonal differences in the thermal sense. Given that the average temperature of the earth is forecasted to rise, studying the effects on the human body from outdoor thermal environments in tropical regions is important for considering how to spend time outdoors in the future. This study clarifies seasonal differences in effects on the human body by comparing the effects on the thermal sensations of the human body from outdoor thermal environments in the winter and the dry season of Bangkok, Thailand in the tropics. The mobile measurements were carried out on the campus of Chulalongkorn University, Bangkok, Thailand. The subjects reported the thermal sensation and the thermal comfort that they experienced while exposed at the observation point. Air temperature, humidity, air velocity, short-wave solar radiation, long-wave thermal radiation, ground surface temperature, sky factor and the ratio of green and water surface solid angles were measured. We found no large seasonal difference between the winter and the dry season in skin temperature due to body temperature regulation. It is clear that in the winter season, people prefer a lower temperature than in the dry season, and in the dry season they tolerate higher temperatures than in winter. The effect of the seasonal difference appears in the amount of change to thermal sensation. We found that it is difficult for seasonal differences to greatly affect the amount of change to thermal comfort. We found that the effect of seasonal difference is that people show stronger responses to thermal comfort for thermal sensation in winter than in the dry season.