Most energy efficiency programs focus on retrofitting or upgrading the equipment. As a matter of fact, maintenance is also a source of energy efficiency improvement. In this article, the performance deterioration of a centrifugal chiller in a hotel is investigated. The result shows that chiller performance deteriorates over time. To restore chiller performance, maintenance actions should be taken. Through chiller performance monitoring, measurement and inspection, the primary cause of performance degradation could be identified. Knowing the causes of deterioration determines what maintenance tasks should be performed. The maintenance interval of the chiller is also optimized to minimize the wasted energy cost. The savings obtained from chiller maintenance is very attractive. In addition, current maintenance tasks are also evaluated for further improvement. To control performance deterioration, potential failure modes must be identified. Based on these failure modes, a new maintenance program is developed.