Integration processes during Mergers and Acquisitions (M&A) phases are very complex and challenging tasks. Managing such a situation poorly would cause negative impacts lasting several years. This is assessed in the decreased on both human resources and operational outcomes. Therefore, to manage the process of the integration in the M&A phases efficiently, key executives engaged with M&A have to consider not only the short-term consequences of a crisis management, but also the unintended consequences for employee attitudes and behaviors that usually negatives during changes. Based on the extensive investigation of related literature in the context of M&A and semi structured interview with key executives experienced with M&A process, corporate cultures integration has been identified as one of the critical factors in the success and failure of M&A exercises.