The present study investigates the relationship between service quality and customer loyalty in one of Iranian banks in province of Golestan, Iran named Bank Melli Iran. The population of the study consists of all customers of this branch. Using Kersity-Morgan table and simple random sampling, a number of 384 customers were selected as the participants of the study. The method of research is descriptive-correlation with a survey design. SERVQUAL scale and a researcher-made questionnaire were used to examine service quality and customer loyalty, respectively. Pearson correlation formula was run to analyze the data. The results showed a significant relationship between different aspects of service quality and customer loyalty in this particular branch of bank.