To ensure the best service and less waiting time, it is necessary for banks to implement Six Sigma. The essence of Six Sigma is the integration of four elements (customer, process, manpower and strategy) to provide management innovation. It facilitates less waiting time, less process length, improving the quality of the services rendered keeping customer satisfaction in mind. In this concern, this thesis has been conducted in four different banks in Sylhet in order to study and analyze the critical factors and expected benefits of six sigma implementation in Banks. The objective of the research is to identify and rank among the critical factors and expected benefits according to their criticality for the successful implementation of Six Sigma in banks.