The present study aimed to explore the effect of EFL teachers’ autonomy supportive behaviors on Iranian EFL learners’ readiness for autonomy. To this end, readiness for autonomy questionnaire (RFAQ) was administered to 240 intermediate EFL learners at five language institutes in Kermanshah, Iran. Then, the researchers trained four EFL teachers based on eight autonomy supportive strategies of self-determination theory (SDT) and devided the participants to two groups of 120 EFL learners. Afterwards, trained teachers attended their classes using the SDT autonomy-supportive strategies. RFAQ was administered to both experimental and control groups for the second time six months later after the experimental group experienced autonomy supportive behaviors. The data analyses revealed that EFL teachers’ autonomy supportive behaviors resulted in an improvement in the five domains determined in the learners’ questionnaire: learners’ acceptance of more responsibility, knowledge about themselves as learners, better knowledge of learning context, a better command of learning process, and more self-initiated learning activities. Implications are discussed.