This research has studied and ranked the service quality and its relation with customers' satisfaction in a bank in Iran. In the theoretical principles section, the concepts and definitions related to services, satisfaction, banking and research background have been studied. The statistical community of the study was all the bank customers that have referred to the bankand have had interest-free loans savings accounts or current accounts. The study statistical sample was calculated using the formula; then a questionnaire was designed and distributed among sample members and finally, the research hypotheses were examined using collected data. Pearson correlation coefficient test was used to test the first hypothesis and specifically related hypotheses. Also, the Friedman ranking test was used to test the second hypothesis. The first hypothesis test results showed that there is a positive and significant relationship between service quality and customers' satisfaction. The second hypothesis test results also showed that there are significant differences among the priorities of the constituent elements of service quality.