This study determined the effectiveness of mindfulness training on ego strengths and metacognitive beliefs of the students. Research method was quasi experimental. Statistical population of this study included all the students of Islamic Azad university of Karaj, (30000 people in 2017-2018). Thirty students were selected using available sampling and randomly assigned to experimental and control groups. The psychosocial inventory of ego strengths by Markstrom et al., (1997) and the metacognitive beliefs questionnaire of Wells & Cartwright-Hatton. (2004) distributed among the participants in both groups. Then, Mindfulness training applied in eight two-hour sessions for experimental group while control group did not take any medical or psychological treatment. After Mindfulness training intervention, the questionnaires redistributed among groups. After analyzing the data by covariance test and variance analysis using 21st version of spss software, results indicated that mindfulness has a significant effect on metacognitive beliefs. In addition it has effect on its subscales (uncontrollability and danger, positive beliefs about worry, cognitive self-consciousness, cognitive confidence, need to control thoughts) and on the ego strength and its subscales, (hope, will, purpose, competency, love, care and wisdom) (p < 0.05) except fidelity (p > 0.05). Although the mean score for fidelity component was increased but it was not statistically significant.
