This study examined the Iranian EFL learners’ multicultural developmental trend in light of Investment Hypothesis as they furthered their academic studies from BA toward postgraduate levels. In so doing 117 BA, 92 MA, and 35 Ph.D. EFL students at AllamehTabataba’i University, Tarbiat Modarres, and Islamic Azad Universities, Tehran, Iran, were randomly selected to provide answers to Multicultural Personality Traits Questionnaire (MPQ) that measures individuals’ Multicultural Personality Traits (MPTs: Cultural Empathy, Open-Mindedness, Social Initiative, Emotional Stability, and Flexibility). Ph.D. students’ MPTs mean was found to be 277.77 MA students’ MPTs mean score was 272.20 and BA students’ MPTs mean score was 267.96.  The ANOVA conducted revealed that EFL Iranian students’ MPTs improved as they furthered their academic career from BA to MA and from MA to Ph.D. levels. The study concluded that advancement in EFL students’ academic career resulted in a concomitant development in their MPTs and among the five MPTs, cultural empathy and social initiative were found to have been significantly improved at Ph.D. level. Among the MPTs, Social initiative provides the highest contribution to social interactions and its significant development at Ph.D. level is confirmatory of the discursive-constructionists’ approach to L2 learning.