Objectives: This study was performed to determine the effects of decreasing ambient temperature on peripheral blood flow and body temperature of males and females in a thermal neutral zone for references to the thermal standard of office workers.Methods: Peripheral blood flows of the hand and feet, and body temperatures and so on of male and female subjects were measured in a climatic chamber. Air temperature was maintained at 28.5°C at the beginning. After this, air temperature was decreased linearly to 21.0°C over a period of 60 minutes. Finally, air temperature was maintained at 21.0°C.Results: Blood flows and skin temperatures of male and female subjects became similar or showed no significant difference at beginning and the end of the experiment. Skin blood flow of the hand and skin temperatures of the hand and fingers decreased, and these values in females were lower than in males, when air temperature was decreased linearly in a thermal neutral zone. However, there were no remarkable differences between males and females in sublingual and mean skin temperatures during the experiment.Conclusion: Minimum air temperature at the thermal standard for offices in Japan is 17°C, which may be too low to be comfortable or neutral. Even in a neutral thermal condition, it is better that office workers are provided some protection such as a blanket or clothing, to protect peripheral body parts from cooling in winter, as there are individual differences in physiological thermal reactions.