The present study has aimed at delving the code of ethics in testing in English language institutions to see how far adhering to these ethical codes will result in EFL teachers' professional behavior. Therefore, 300 EFL instructors teaching at English language schools in Khorasan Razavi Province, Zabansara Language School, as well as Khorasan Shomali Province, Kish Air and Fatemi Language Schools were selected randomly to fill out two questionnaires, Professional Behavior Inventory as well as Code of Ethics in Testing Inventory. Moreover, a structured interview was employed among the participants of the study, 30 instructors, to obtain a more in depth data. After the qualitative and quantitative results were analyzed by running Multiple Regression, it was revealed that "Considering Content" as one of the subcategories of code of ethics in testing could be considered as a significant predictor of teachers' professional behavior. Finally, limitations of the study and suggestions for further research are discussed.