Increasing market share as one of the goals of the organization wouldn't happen without increasing the customer’s satisfaction of through improving service quality. The present study sought to examine the level of service quality offered in one of the subsidiary of BSI and solutions for improving the quality of service at this branch. The application of this study is base on survey method. In this study, the clients of BSI branch are under experiment. Because the clients are unlimited we used Cochran formula, share questionnaires to 170 people and calculate the result based on 0.11 variance. Techniques used in analyzing the data of this research consist of: gap analysis model to identify gaps between expectations and perceptions of service quality elements of the bank's customers, Kano model, this study aimed to identify needs and offer attractive solutions to improve them , Quality Function Deployment Model used To provide strategies for improving the performance and set priorities for action identified by the Kano model and improving them. To avoid ambiguity in quality matrices of the data of this research, Rough set theory was used. The result of analyzing data shows that each of 29 components has gaps and the Result of Kano model indicate that 9 components assumed attractive. In order to promote the quality of services in this branch, base on the view of authorities, 10 technical features were identified and prioritized.