Even though there is a large body of knowledge related to buildings, only a limited number of examples with a focus on asset management exist in published literature. More importantly, current literature lacks rating systems that support tactical and operational management of building infrastructure. This paper addresses the aforementioned knowledge gap and building industry requirement by proposing an index for operational management of a public building using building level of service (LOS). In the context of buildings, LOS is defined as an assessment of the operational performance provided to building users, society, and the environment. A fuzzy synthetic evaluation (FSE)-based method was used to assess the LOS of buildings. First, key performance categories and indicators were defined for operating building performance assessment. Indicators and benchmarks were customized for an aquatic centre building. A case study was conducted to demonstrate the application of the LOS index. Results from this approach provides an assessment of the operational performance of the aquatic centre building with respect to nine LOS performance categories. Overall building LOS was evaluated as good for the three pseudo scenarios considered. The proposed LOS index facilitates asset management of public buildings by providing information for operational, tactical, and strategic decision making.