AbstractThermal perceptions and preferences of individuals outdoors cannot be entirely explained by the energy balance of the human body. They are also affected by psychological and behavioural factors or the so‐called thermal adaptation. To examine the effect of thermal adaptation on seasonal outdoor thermal comfort, 1644 interviews with concurrent micrometeorological measurements were conducted outdoors in central Taiwan. Results indicate a deviation of 1.3 °C standard effective temperature (SET*) in neutral temperatures between hot and cool seasons, and a deviation of 1.8 °C SET* in preferred temperature between hot and cool seasons. Additionally, although subjects' temperature and sunshine preferences were highly correlated with SET*, they diverged between seasons for identical SET* exposures in the two seasons. Analysis reveals that people's thermal perceptions were strongly related to the air temperature (Ta) and mean radiant temperature (Tmrt), but not significant to air speed and air humidity. These results demonstrate that thermal adaptation markedly influences seasonal outdoor thermal comfort, knowledge of which may be useful in the planning and design of outdoor environments in hot–humid regions. Copyright © 2010 Royal Meteorological Society