The purpose of this study was to clarify the effect of working environments of different kinds of commercial kitchens on the thermal strain of kitchen workers. This study design was cross-sectional study, and data collection was performed during busy time in commercial kitchen from August to September 2006. The research subjects were 8 institutions, involving 7 cookers, and 16 men. Measured environmental variables were air temperature, radiant heat index, wet bulb globe thermometer index (WBGT) in front of the cookers, ambient temperature, and estimated ambient WBGT around the workers. The thermal strain on workers was evaluated by fluid loss, body temperatures, heart rate and amount of physical activity (METs). All average estimated ambient WBGTs in front of cookers were less than 27.5℃. The average heart rate was 107 ± 10 bpm, and average METs was 2.0 ± 0.6. The peak values of upper arm skin temperature and auditory canal temperature were less than 37.5℃. The work environments were affected by the kitchen spaces, cooling devices, heating methods, and heat sources. Even in the midsummer, if environmental temperatures were controlled adequately, estimated ambient WBGTs around workers were below the occupational exposure limit. Work environments and thermal strain on workers in commercial kitchen were not severe.