Educating teachers for sustainability requires that teachers be considered as the mediators of change. To achieve this goal, a constructive teacher-learner relationship is essential where values and ethicality play a crucial role. Investigating language teachers' moral identity as an important aspect of teacher cognition can yield useful insights into the kind of relationship which is congenial to the desired whole-person development. The present qualitative study intended to explore the nature of moral dilemmas in language classes and teachers' criterial beliefs in responding to these dilemmatic situations. A systematic coding analysis of the recorded interviews with eight Iranian experienced EFL teachers revealed that they encountered moral dilemmas in both disciplinary and educational aspects of the teaching process. They referred to their knowledge, experience, intuitive sense as well as the teaching context and learners' history as sources of their moral judgment. The findings on teachers' moral identity uphold implications for teacher education.