Customer satisfaction through improving service quality considers a critical sucsess factor in the super service organizations. Because of importance of quality and its effects on customer satisfaction in service industries, the key question is how the quality of services can be evaluated. The aim of this paper to determine the most important factors affecting bank service quality, to calculate and analyze effective factors in bank service quality from view points of bank customers and employees, to analyze the gap between customers and employees' expectations and bank performance and finally to provide the posibility of valid scientific improving bank future performance. Factors affecting bank service quality were defined according to the literature. We also asked bank and academic experts view points to adjust the factors and confirm their validity. To calculate factors relative importance weights, a questionair was designed and distributed among a sample group of customers and employees selected randomly. Results of the statistical analyzes show a meaningful difference between the importance weights determined by customers and employees. Also, there is a meaningful differnce between customers and employees priority concerning corrective measures for better future performance. In addition to statistical analyzes, we measured and evaluated bank service quality using four well known models (SERVQUAL, weighted SERVQUAL, SERVPERF, and SERVIMPERF models). The results imply that in all models, not only both customers and employees scored bank service quality more than average, but also customers average score on bank service quality was meaningfully higher than employees average score. Generally, results of this research provided a set of valuable data to bank in order to improve its service quality in future based on both its customers and employees view points.