AIM: The purpose of the present research was to investigate the mediating role of achievement motivation in the relationship between conscientiousness, role performance, and extra-role performance. METHODS: The research method was correlation and statistical population consisted of all employees of the University of Shahrekord of whom, 157 employees were selected by the convenience sampling method. The Achievement Motivation Questionnaire (Hermanns, 1970), Conscientiousness Inventory (Costa, McCrae, 1992), Role Performance (Patterson, 1963), and Extra Role Performance (Lee and Allen, 2002) were used. Data were analyzed by the Pearson correlation coefficient and structural equation modeling (SEM). FINDINGS: Results revealed that there was a significant positive relationship between conscientiousness and achievement motivation with role performance and extra-role (p<0. 01). Moreover, the proposed model has appropriate goodness of fit, and results of structural equation modeling showed that conscientiousness has a positive and significant effect on achievement motivation, and also achievement motivation has a positive and significant effect on the role and extra-role performance (p<0. 01). CONCLUSION: According to the findings, achievement motivation as a complete mediator was able to mediate the relationship of conscientiousness with the role and extra-role performance. Based on research results, it can be concluded that conscientiousness increases the role and extra-role performance through achievement motivation.