Psychological capital is a new concept that has been discussed in the third millennium and entered in the field of management since 2006 Due to its unique role in organizational wealth-generation, it has become in the core attention of scholars and intellectuals research in the field of behavior, human resource management and human capital. So the main goal of this paper is designing a model to improve psychological capital in Iranianpublic organizations with identifying the role of human resource functions. This research has employed quantitative approach and followed correlation method. The populations for this study were employees of public organizations; the rational for selection of them was classification system in the governmental budget. Accordingly, they were classified into the three categories of general, social and economic. On the other hand, due to the wide dispersion and large organizations across the country, public organizations of Tehran province were chosen as key clusters.
The research method is descriptive correlation study, and the data were collected using standard questionnaires. The data were analyzed by using structural equations and multiple regressions. The research findings showed that HR functions have significant positive relation with the psychological capital; however when organizational justice is placed as the intervening variable between them, the correlation coefficient is increased. The results also indicated that HRM functions have the greatest effect on Psycap by organizational justice. At last, fitness test of the model demonstrated that it is suitable for Iranian public organizations.