A Post-Merger Integration process is a difficult and complex task. It consists of a long list of requirements and activities that have to be fulfilled within a short period of time. There are many opportunities to exploit and many decisions to take. The aspired goal in Post-Merger-Integration processes is the full integration of the acquired company,1 which consists of certain integration measures such as strategic, organizational, personal and cultural incorporation. Hence, the integration focuses on the bringing together of companies and their activities concerning alignment of merging individual divisions or departments within the two companies to a new and successful operating unit.2 A merger and its cultural integration are to be understood as a long term process, where a large number of characteristics of the company such as values, language, actions or behaviors are involved. Considering these aspects, the readers of this thesis will understand the impact of the corporate culture on a Post-Merger-Integration strategy. Therefore this paper will examine, amongst others, the following research question: “What role does the corporate culture play in the implementation of a Post-Merger-Integration, by considering the case studies on the mergers of mobilkom Austria AG / Telekom Austria TA AG and Orange Austria Telecommunication GmbH / Hutchison Drei Austria GmbH?” In order to figure out the required answers to this question, this thesis will analyze in the first part the main theoretical views of Post-Merger-Integration processes and corporate culture. Taking into account the above mentioned different theoretical aspects, the reader will be introduced to practical examples from the Austrian telecommunication industry. The objective of this paper is to understand the impact of the corporate culture by considering the above mentioned case studies within a Post-Merger-Integration phase. This study will generate its information via high-valued literature, journals and articles related to this topic. The practical examples are based on an empirical study, which was acquired by qualitative interviews.