Research on cross-sector collaboration has grown over the past decade. This model of collaboration brings organizations in two or more sectors together, to link or share information, resources, activities and capabilities when no single organization has enough time, money, knowledge or authority to address them alone. In a post-disaster period, the governmental organizations particularly in developing countries usually are unable to provide all necessary services alone; hence, collaboration with other agencies is required. In the last decades, studies have used the viewpoint of collaboration between NGOs and the government, and shown a beneficial relationship between them. Most studies have focused on the structures of the collaboration in the aftermath of disasters with hierarchies, protocols, authoritarian roles and the standardization of procedures but there is a gap in analysing the process factors and the interaction of process and structural factors influencing the collaboration during post-disaster period. In this study, the aim is to identify the main factors of process and structures influencing the collaboration between Iranian government and NGOs after the earthquake in Bam city in Iran in 2003. Analysing the content of the previous studies showed that lack of experience on how to deal with disasters and unclear tasks as well as insufficient trust and mutual understanding between the actors were the main reasons of failure in collaboration. The lack of specific organizational tasks at a given time led to exacerbate the tension in the process of working together; increase the lack of common understanding, and fail to achieve the mutual goal.