In recent years, Japan has seen a sharp increase in foreign cross-border merger and acquisition (M&A) transactions. Among the larger cross-border M&A transactions in Japan, a few multinational companies are already struggling with their acquisitions. In this study, we systematically analyzed and compared the unsuccessful DaimlerChrysler-Mitsubishi acquisition with the successful RenaultNissan acquisition. We collected secondary data and conducted interviews with both Japanese and foreign managers. Despite some similar starting conditions, these acquisitions developed widely divergent outcomes. In this study, we have focused on post-acquisition integration and separated it into human integration and organizational integration. Findings indicate that human and organizational integration are strongly interwoven in Japan, with human integration being a necessary prerequisite for organizational integration. These findings highlight the importance of the human factor in the success of acquisitions. Active communication, participation, assertive leadership, commitment and the creation of a sense of urgency have been found to facilitate human integration. With regard to organizational integration, the autonomy of the integration management and independence from any keiretsu network have been identified as important factors.