This quantitative study aims to examine the relationship between EFL teachers' professional development (PD) and their self-efficacy in online education during the COVID-19 pandemic. The participants of this study were 80 English as a foreign language (EFL) teachers selected via convenience sampling who were teaching online in different schools in some cities of Iran. In order to gather the data needed for the study and to measure the variables of the study, two different types of closed or Likert questionnaires were administered. One was a questionnaire to measure various aspects of PD, and the other was a long form of teachers' sense of efficacy scale (TSES) to examine teacher self-efficacy. To answer the research questions, Pearson correlation coefficient linear and multiple regression were run. The results revealed that there was a positive significant relationship between teachers' self-efficacy, knowledge, skills, and the teacher professional development (TPD) program. The results also showed that among the components of the TPD, knowledge and skills were significant positive predictors of self-efficacy and the TPD programs cannot significantly predict teacher's self-efficacy (p>0.01). Therefore, teacher professional development can predict teachers' self-efficacy. Finally, some findings and implications are presented.