No / The complexity of sustainable building maintenance environment enforces organizations to develop a standardized maintenance quality management system that can be applied in all concerned departments. This Chapter presents a novel conceptual model of a hybrid Knowledge-Based Lean Six Sigma Sustainable Building Maintenance System (Lean6-SBM). The KB model seeks to apply the Lean Six Sigma philosophy to support implementation of an ideal building maintenance system. The conceptual KB model also integrates GAP technique to support benchmarking and decision making. The proposed conceptual model is presented to show the fundamental components of the Lean6-SBM. / This work was supported by the Ministry of Defense Engineering Services 403 (MoDES—Sultanate of Oman) and the University of Bradford (United Kingdom).