To determine the optimal thermal environment for dialysis rooms, field measurements and questionnaires to dialysis patients and medical staff were conducted during autumn and winter. The mean air temperature fluctuated between 22.4°C and 27.1°C in autumn and between 21.6°C and 25.1°C in winter. The fluctuation of the mean radiant temperature coincided with that of the air temperature. The mean relative humidity was below 50%, and air velocity was below 0.17 m/s in both seasons. The survey showed that 29% of patients and 61% of staff required an improvement in the thermal environment. A statistically significant difference was observed between the thermal sensations of patients and staff in both seasons. It was revealed that the patients maintained neutral thermal sensations by using electric blankets in both seasons. However, development of an alternative to this method in the case of dialysis patients is recommended because arranging the blankets would be burdensome for nurses.