Identity formation is one of the main concerns of today’s education and can have a vital role in ESP learners’ future professional success. This study investigated whether the employment of interactive practices in ESP courses had any impact on the identity formation of introvert students. Initially, 200 undergraduate students majoring in Computer Sciences, Accounting, and Physical Education answered the introversion/extraversion section of the Myers-Briggs Type Indicator (MBTI) and Cheek and Briggs’ Aspects of Identity Questionnaire (AIQ-IV). Based on their performance on MBTI, 90 learners with the extravert, introvert, and non-discriminating personality traits were selected from six classes and formed the three Extravert, Introvert, and Control (n1=n2=n3=30) groups. The students had taken a Specialized English course in the second semester of their BA program. The classes lasted 14 sessions. During the treatment, the researchers employed different activities for teaching ESP. After the instruction, the participants took the AIQ-IV. The results of ANCOVA indicated that the Introvert group gained significantly higher scores on the identity questionnaire than the Extravert and Control groups. The results of paired samples t-tests showed that while introverts had improved considerably in all components of the identity questionnaire, the Extravert and Control groups did not show any changes. The findings indicated that in interactive classroom environments, introvert learners had more inclination than the extravert and mixed introvert and extravert learners toward a shift in identity. The study has implications for ESP teachers, practitioners, and educators.