Abstarct: This study examined how collaborative professional development (CPD) relates to self-efficacy of the high school English as a Foreign Language (EFL) teachers. Even though there is a growing recognition that self-efficacy among teachers is a highly important factor that defines the quality of teaching and student performance, there is still a noticeable high number of EFL teachers who purport that their confidence levels regarding the use of new teaching methods are very low. In the study, research also was geared towards exploring the application of the CPD activities such as peer observation, reflective dialogue, and team teaching and its effects on enhancing the beliefs of the teachers in their instructional and classroom management as well as student engagement skills. The mixed-methods approach was adopted: quantitative data will be collected using an instrument named a teacher self-efficacy scale that was administered to the EFL teachers that was selected in the high schools, and the qualitative data collection method was a semi-structured interviews and focus groups discussion aimed of learn more about the experiences and perceptions of the teachers. The quantitative analyses showed that there were significant positive correlations and predictive relationships between CPD dimensions and teachers’ confidence in the instructional, managerial and engagement domains, whereas the qualitative results provided further evidence of the experience and perceptions of teachers on collaboration. The findings showed how collaborative learning communities help them in their professional development, share and practice reflexivity with one another. The study relied on empirical data which was utilized to construct effective patterns of professional growth in the environment of EFL which will ultimately translate to improved teaching outcomes and student performance.