Background: Recently, positive character strengths-based interventions have had very effective results on increasing wellbeing in numerous studies in different parts of the world. However, in Iran, localized, strengths-based interventions have not yet taken place. Aims: The aim of the present study was to evaluate the effectiveness of character strengths training on solidification of character strengths and increasing students' mental wellbeing. Method: This study was performed as an experimental research with a quasi-experimental design on students of the University of Tehran. The sample size of this study was determined according to the number of groups and the number of variables studied, 28 people (at least 14 people in each group). Participants answered Mental Wellbeing Questionnaire and Character Strengths Questionnaire (Iranian version) in three rounds including pre-test, post-test and follow-up. Results: The results of repeated measures analysis of covariance showed that in the experiment group, the scores of wellbeing components and character strengths were higher than the control group. The observed changes in the experiment group at the follow-up stage were also somewhat stable. Conclusions: Based on this, it can be concluded that the package developed for improving character strengths has an effective role in increasing these strengths and mental wellbeing. Key words: Character strengths, positive psychology, culture, wellbeing