An absorption chiller/heater has drawn much attention because it doesn't use CFC and works by poor quality heat source. In cooling operation of an absorption chiller/heater, an outlet temperature of chilled water is needed to be controlled accurately even under disturbances such as changes of cooling load. This paper proposes the control system with parameters adjusted by fuzzy inference to supply chilled water stably. Moreover this paper presents the experimental result of applying the proposed control system to an absorption chiller/heater.