<p>Teacher educators have scrutinized various ways to advocate the nonlinear and multifaced process of teachers’ learning. However, they still struggle with determining teachers’ capabilities in transforming their agency while facing challenges and requirements of present time. To that end, the current study intended to design and validate an assessment inventory which pointed at evaluating student teachers’ transformative agency. The study was carried out in two phases. A semi-structured interview and comprehensive literature review were used to set the fundamentals and theoretical principles of the study. Grounded on the results of the first part, cultural historical activity theory and transformative agency classification were employed for generating a 40-item questionnaire on 5 Likert scale. In the second phase, the main data collection procedure was preceded by a pilot study. Two sets of exploratory factor analysis and confirmatory factor analysis were employed to investigate the psychometric characteristics of the questionnaire. The results of the first exploratory factor analysis led to 7items exclusion and the other analysis outcomes represented acceptable level of reliability. Moreover, the questionnaire showed a good level of fit. Researchers, student teachers and teacher educators can take advantage of the outcome of this practice.</p>