A Thesis Submitted to Mzumbe University, Dar es Salaam Campus College in Partial Fulfillment of the Requirements for the Award of Masters Degree of Business Administration in Corporate Management.Customer service is the provision of caring the customers before, during and after a purchase. It is a series of activities designed to enhance the level of customer satisfaction – that is, the feeling that a product or service has met the customer expectation." The general objective of the research was investigating customer satisfaction and performance of commercial banks in Tanzania particularly was done at NMB PLC in Dar es Salaam Region. Specifically the study was identifying types of service delivered to customers by NMB PLC in Tanzania; determine the challenges facing NMB on customer service delivery in Tanzania; and investigate the perception of the customers on the service delivery by NMB PLC in Tanzania. This study found that, in the changing and speedy environment of NMB Ltd bank must identify and update the expectation of the stake holders and can try to satisfy their maximum needs. Moreover, the study recommended that all staff at NMB PLC should assure customers that any personal information or details given or held in records is treated with the strictest confidence, also the staff at NMB PLC should seek the consent of the customer before disclosing information either internally or to other agencies and then only on a strictly need to know basis. The staff must assure customers that all staff and other agencies receiving confidential information observe the same levels of confidentiality. Then staff must ensure that interviews and conversations with customers about personal, confidential or contentious issues are carried out in private and not in reception or other public areas.