The main purpose of this research is to evaluate the indoor environmental qualities and productivity in an energy-saving building. Field surveys were conducted in the office building to study the indoor environment and the workers' behavior. At the same time, the satisfaction vote of the indoor environment and self estimated productivity were investigated by questionnaire survey. The target office building was designed and constructed to be energysaving building twenty-nine years ago. It had already been revealed that the energy consumption of this building was low as it had been designed. As a result, we confirmed that the indoor environmental quality of this office was maintained at good levels. On the other hand, some workers of this office were dissatisfied by thermal environment. Further consideration of these points could lead to improvement of workers' productivity.