The importance of emotional aspects and paying attention to teachers' activities from spiritual and emotional perspectives to prevent work burnout and strengthen professional learning in this occupational group is well recognized. This study aimed to ascertain how the agency of Iranian EAP instructors relates to their professional development, burnout, and adaptive expertise (AE). Additionally, it examined how well Iranian EAP instructors’ agency predicts their level of burnout, professional development (PD), and adaptive expertise. Thus, the researcher employed questionnaires as the method of data collection. One hundred twenty-two Iranian EAP teachers were asked to complete the Teachers’ AE, PD, Burnout, and Teacher Agency questionnaires via convenience sampling. The reliability of the translated versions of the utilized questionnaires was confirmed by Cronbach's alpha. Various statistical measures, including correlation, regression, and ANOVA (F(4,117) = 12.506, p = 0.000), were applied to draw inferences from the observed data. The findings demonstrated a significant and positive correlation between professional development and overall teacher agency. A significant positive correlation was found between Iranian teachers’ AE and agency. Iranian teachers’ burnout and their optimism, one of the agency components, were found to have a negative but statistically significant correlation. These study findings offered empirical evidence about the agency of Iranian EAP instructors and also revealed the predictive function of teachers’ agency in describing their AE, professional growth, and burnout. The findings of the research can be helpful to everyone involved in language acquisition, including educators, researchers, and teachers.