The importance of the post-merger integration (PMI) is derived from the fact that the value creation can only begin when the organizations begin to work towards the purpose of the acquisition. Besides merger, another source of radical change in a company’s life cycle is the implementation of an enterprise system (ES), such as ERP. Both mergers and acquisitions and enterprise systems implementation miscarry frequently. In this paper we study the post-merger integration of the enterprise systems (ES) by testing the Motwani et al. (2002) Framework for ERP Implementation that is based on Business Process Change Theory in this context. We conclude that besides change management, issues relevant to successful post-merger ES integration include: M&A factors, factors related to company expertise & resources and factors related to software & vendor. Furthermore, an important notion is that different units may require different managerial approaches or different amounts of resources because of the possible differences in there IS capacities and readiness to change.