This study aims to examine the effect of knowledge, promotion, and religiosity on the interest in using Islamic banking services. The purpose of the next research is to examine the effect of knowledge on religiosity. In addition, this study also examines the effect of educational background and age on saving interest in Islamic banks. The population in this study are customers of Bank Syariah Mandiri, Brebes, Central Java, Indonesia. Ninety-nine research samples were obtained. The data collection method used was questionnaires. The data analysis method used was SEM-PLS. The results showed that only promotion proved to have a positive and significant effect on interest in using the services of Islamic banks. Knowledge and religiosity have not been proven to have a significant effect on interest in using services of Islamic banks. Likewise, background and gender do not have a significant effect. The next research result is that there is a positive and significant influence of knowledge on religiosity; there is also a positive and significant influence on the promotion of knowledge. This study recommends the importance of continuing socialization and education from Islamic banking stakeholders in Indonesia to continue introducing Islamic banks to the public.