Six Sigma has been adopted in various industries as a set of practices for improving manufacturing processes and eliminating defects of the company. Incorporating with the Lean Manufacturing practice, the Lean Six Sigma concept was applied further to the service sector in order to raise the company’s quality of services. Albeit a significant amount of service businesses were nominated in numerous Six Sigma Awards across the globe, the Lean Six Sigma concept is a new and adventurous set of practices facing the service industry. This article, thus, presents the Lean Six Sigma concept along with a case study of its implementation to improve business processes using the case of Thai Military Bank Plc. (TMB).