The merger integration process in one of the most critical stages of the deal, and getting a good price is important, but not as important as making sure the deal works. There have been several theses discussing the merger process as well as the importance of post-merger integration, focusing on culture melding or financial system synergy. This study focuses on the post merger integration process of a subsidiary of MNC in Taiwan. The parent company in the past few years have acquired two MNCs and experienced two large global scale integration processes in which the Taiwan subsidiary followed the HQ directives to undertake acquisition integration of the two acquired firms’ local subsidiaries. The integration of two other local subsidiaries provides a rare opportunity to investigate the post-acquisition process occurred in a MNC context. The finding throws light on the post-acquisition process at the subsidiary level and how the process related to the parent’s global strategy of merger and acquisition. All three subsidiaries involved are mainly marketing and sales organizations. Therefore, this study would focus on the integration of marketing and sales functions. This study chose the case study research methodology because the pharmaceutical industry is the industry the research is most familiar with and there is no other case, either a subsidiary or a company, having experienced similar M&A. The researcher found the case company-subsidiary is a unique one, because of the two M&A it experienced, presenting a rare opportunity for studying M&A at subsidiary level. The case study approach investigated deeply the two complete M&A integration process. The case study approach relies on researching the parent and subsidiary history, academic literature on M&A, and in-depth interview with key executives of the subsidiary to identify key activities and decision points in the whole integration process. The research discovers that successful melding of cultures and integration of product management helps post-acquisition growth, and organizational learning played a key role in utilizing the first M&A experience to accelerate the subsequent merger-integration activities. Key words: Merger/ Acquisition, Post-merger integration, Product management process / The merger integration process in one of the most critical stages of the deal, and getting a good price is important, but not as important as making sure the deal works. There have been several theses discussing the merger process as well as the importance of post-merger integration, focusing on culture melding or financial system synergy. This study focuses on the post merger integration process of a subsidiary of MNC in Taiwan. The parent company in the past few years have acquired two MNCs and experienced two large global scale integration processes in which the Taiwan subsidiary followed the HQ directives to undertake acquisition integration of the two acquired firms’ local subsidiaries. The integration of two other local subsidiaries provides a rare opportunity to investigate the post-acquisition process occurred in a MNC context. The finding throws light on the post-acquisition process at the subsidiary level and how the process related to the parent’s global strategy of merger and acquisition. All three subsidiaries involved are mainly marketing and sales organizations. Therefore, this study would focus on the integration of marketing and sales functions. This study chose the case study research methodology because the pharmaceutical industry is the industry the research is most familiar with and there is no other case, either a subsidiary or a company, having experienced similar M&A. The researcher found the case company-subsidiary is a unique one, because of the two M&A it experienced, presenting a rare opportunity for studying M&A at subsidiary level. The case study approach investigated deeply the two complete M&A integration process. The case study approach relies on researching the parent and subsidiary history, academic literature on M&A, and in-depth interview with key executives of the subsidiary to identify key activities and decision points in the whole integration process. The research discovers that successful melding of cultures and integration of product management helps post-acquisition growth, and organizational learning played a key role in utilizing the first M&A experience to accelerate the subsequent merger-integration activities. Key words: Merger/ Acquisition, Post-merger integration, Product management process