Abstract Merger is one of the most important changes that organizations experience. This change can have many effects and different aspects. The purpose of this research, is examination of the effect of merger on organizational identification and organizational legitimacy. Our society is the Ministry of Cooperatives labour and social welfare. In this regard, changes of organizational identification and organizational legitimacy before and after the merger have been studied. In this research, organizational identification has been studied based on expanded model of organizational identification (Misidentification, Ambivalent Identification & Neutral Identification); this means that the effect of merger on these types of organizational identification has been studied. In addition the impact of organizational legitimacy on organizational identification and misidentification, ambivalent identification & neutral identification, after merger has been studied. Finally the solutions for improving organizational identification have been presented based on the results.   The results of the research show that in the ministry, the organizational legitimacy and organizational identification decreased significantly after the merger compared to before the merger, but misidentification, and ambivalent identification have increased significantly, although the changes of neutral identification was not significant. Based on the results of the post-merger phase, it was revealed that organizational legitimacy has a direct impact on organizational identification and has an inverse impact on the 3 types of organizational identification based on expanded model of organizational identification.