This explanatory research uses a mixed method design to investigate the effect of using an online community of practice within teaching practices on science and math pre-service teachers' teaching self-efficacy beliefs. 102 science and math pre-service teachers participated in the research. "Teaching Self-Efficacy Belief Scale" and "The Questionnaire on Opinions about Using Online Communities of Practice within Teaching Practices" were the data collection tools of the study. Results showed that online communities of practice affected pre-service teachers' teaching self-efficacy beliefs significantly and positively. Qualitative data of the research also supported this positive change. Science and math pre-service teachers mentioned several benefits of online communities of practice, such as sharing, recognizing common problems, freely expressing themselves, making comparison, realizing their shortcomings, and benefiting from the experiences of others. However, research findings also showed that online communities of practice have some limitations such as the lack of expressions of sincerity, the need for internet access, the need for additional time, and anxiety when it comes to criticism.