Abstract Hypobaric conditions, with pressures about 30% below that at sea level, are often experienced at mountain resorts. The diffusive transfer of water evaporation increases at hypobaric conditions whereas dry heat loss by convection decreases. Two experiments were conducted to clarify the interactive effects between barometric and thermal events on man's thermal comfort. The experiments were conducted in a decompression chamber where the temperature was controllable. The temperature conditions were set at a constant 26°C or 30°C with 50% RH and 0.1 m/s airflow. The barometric conditions were examined stepwise for 1000, 2000, 3000 and 4000 m of simulated altitudes, which were held for 20 min at 26°C and 40 min at 30°C, respectively. Three male adults, lightly clothed, participated in each experiment. They remained sedentary for about four hours in the chamber. Thermal sensations were measured at each altitude with SD-rating scales. Subjects were also required to complete an introspection. The main results are as follows: when the altitude rose, (1) the heart rate increased for both temperature conditions: the increment at 26°C seemed to be based on hypoxia; (2) the skin temperatures of face and trunk were higher than those of extremities for both experiments; (3) thermal sensations for the face and trunk became warmer for both experiments, so subjects found it difficult to express their thermal state. Therefore, it is supposed that the blood flow in the body would change to compensate for hypoxia under hypobaric conditions.