Cataloged from PDF version of article. Thesis (Master's): Bilkent University, M.A. in Curriculum and Instruction, İhsan Doğramacı Bilkent University, 2023. Includes bibliographical references (leaves 74-85). The present experimental study tested whether inducing English language instructors’ autonomous or controlled motivation and their fixed or growth mindset about teaching ability influence their autonomy-supportive versus controlling teaching style. A hundred and fifty-six English language instructors working at the preparatory programs of state and non-profit foundation universities in Turkey participated in the study. The results of t-tests showed that participants in the autonomous motivation and growth mindset conditions endorsed their conditions to a larger extent than the teachers in controlled motivation and fixed mindset conditions. However, Factorial ANOVA indicated that neither the main effect of each condition nor the interaction of the conditions predicted the participant English language instructors’ autonomy-supportive or controlling teaching style. Furthermore, supplementary analyses revealed that teachers from non-profit foundation universities and younger teachers reported higher autonomy-supportive teaching style than teachers from state universities and older teachers. The findings are discussed in terms of their methodological and educational implications. by Vahide Teke Akay M.A.