This study aims to determine the influence of the basic principles of Islamic Business Ethics; fairness, free will, responsibility, and truth to Customer Retention (A case study of Bank BTN Syariah Branch Yogyakarta). The sample in this study is taken by using purposive sampling technique (nonrandom), with the number of samples as many as 100 respondents from Bank BTN Syariah Branch Yogyakarta. Data analysis in this study uses quantitative and qualitative. The hypothesis is tested using F test which shows that the basic principles of Islamic Business Ethics as an independent variable which after the research has been proven simultaneously have a positive and significant influence on customer retention. Furthermore, through the t test, it can be seen that the variables of fairness, free will, and truth have a positive effect on customer retention, while the responsibility has a negative effect on customer retention. The coefficient of determination test (R2) shows the result that 37.1% which affecting customer retention is explained by the variables of fairness, free will, responsibility, and truth.