The purpose of this paper is to assess the solar radiation load on thermal comfort in outdoor thermal environments. An urban street canyon and an open space were selected as sites for field survey. Outdoor climatic conditions, subject's thermal sensation and skin temperatures were measured on the sites for a few day in summer, autumn and winter. A modified mean radiant temperature was introduced to indicate the effect of solar radiation and radiation interchange between outdoor objects on the human body. An operative temperature and a standard operative temperature were calculated based on the modified mean radiant temperature. There are high correlation between the operative or standard operative temperature and thermal sensation or mean skin temperature. Those indices, especially the standard operative temperature, are considered to be effective in the outdoor environment.
