OICC Press Journal of New Trends in English Language Learning (JNTELL) 2821-2290 3 5 2025 02 23 Unraveling the Impacts of Teacher’s Self-Disclosure on Idiomatic Expression Learning and L2 Willingness to Communicate among EFL Learners 10.71528/2024.1195652 EN Masoud Taheri Department of English Language, Shahreza Branch, Islamic Azad University, Shahreza, Iran Mohsen Shahrokhi Department of English Language, Shahreza Branch, Islamic Azad University, Shahreza, Iran Mohammad Reza Talebinejad Department of English Language, Shahreza Branch, Islamic Azad University, Shahreza, Iran Journal Article 2025 02 23 While research on teacher self-disclosure (TSD) has been expanding, its specific effects as a teaching strategy on English as a Foreign Language (EFL) outcomes in Iran have not been thoroughly investigated. This study aimed to explore how TSD influences EFL learners, focusing on their comprehension of idiomatic expressions and their willingness to communicate in a second language (L2 WTC). Employing a quantitative, quasi-experimental design, the research involved a non-random sample of 99 EFL teachers and 64 upper-intermediate learners from Isfahan and Chahar-Mahal provinces. Data were collected using a scale measuring teachers’ self-disclosure, a test for idiomatic expressions, and an L2 WTC questionnaire, all demonstrating strong reliability and validity. The findings revealed that EFL teachers frequently engage in self-disclosure, with this practice linked to various demographic factors. Notably, a hierarchical multiple regression analysis indicated that, apart from gender, teachers' educational background, teaching experience, and age significantly influenced their tendency to self-disclose. Furthermore, the study showed that TSD had a positive impact on learners’ willingness to communicate and their understanding of idiomatic expressions. These insights underscore the importance of fostering positive teacher-student relationships, enhancing EFL learning outcomes, developing effective instructional materials, and creating professional development programs for EFL educators.