The objectives of this three-year research project are to quantify the effect of thermal environment on office workers’ performance, to evaluate the productivity of introducing COOL BIZ in office, and to discuss the favorable indoor environment of 28oC office both in terms of the economical effect and the conservation of energy. The major outputs include: (1) the Productivity Evaluation Tool, which enables to collect data in the web server was developed; (2) from the two subjective experiments, the relationships was obtained that the level of fatigue is higher and the performance is lower in the indoor environment which is evaluated to be more dissatisfied with thermal environment; (3) it was pointed out through the field survey of an office undertaking COOLBIZ that there was an uneven distribution of temperature in the office, that the HVAC systems require adjustments for the proper operation, and that there were more than 70% of occupants who was thermally dissatisfied; and (4) the conservation of energy in a typical office building for raising the preset temperature by 2oC is estimated to be 1.64%.