The present study has examined the effect of psychological capital on organizational citizenship behavior. This is a case study with cross-sectional design and questionnaire as research method. Statistical population was the formal and contract staff of the Ministry of Youth and Sport (N=210 Employees). The data related to psychological capital and organizational citizenship behavior variables are gathered via Luthans et al. (2007) and Podsakoff et al. (1994) standard questionnaires. The reliability of the standard questionnaire was measured by CR and AVE tests and the validity of that was measured  by confirmatory factor analysis via Smart PLS Software. The questionnaire distributed among 160 employees that those selected randomly. Data analyzing was performed by Smart PLS and XLSTAT via structural equations method (SEM). The results show that psychological capital has a positive and meaningful impact on organizational citizenship behavior. We also showed that the most impact of dimensions of psychological capital on organizational citizenship behavior (R²:0.35) is made by altruism dimension.