According to the information, the value of corporation acquired in global mergers amounted to US$4 trillion. Last year the biggest merger & acquisition was the AT&A bought the BellSouth Group in US for US$860 billion. After 1990, the corporate mergers & acquisitions become a main magic tool of a company to strengthen its market competition. Examples of same industry mergers were: Glaxo Wellcom PLC bought SmithKline Beecham PLC & Pfizer with Warner-Lambert in Pharmaceutical industry Daimler Benz bought Chrysler in vehicle industry Compaq with Digital in high technology industry Seibu Group with Itochu in Supermarket industry Bank of Tokyo with Mitsubishi Bank in banking industry Taiwan Mobile with Columbia in communication industry The diversification of M&A such as: Viacom with CBS Corporation The famous Canadian wine group ¡V Seagram acquired the well-known Asian company Polygram Musical Company at US$106 billion America Online with Time Warner. The above illustrated that the M&A in the diversification and related industry has become a trend and as vital element in the main tool to enhance market competition. In 2002, the figure showed the total global value in M&A was US$1.1 trillion. Regionally, the M&A trading in Europe, US and Japan (excluding other Asian countries) were US$1.5 trillion, US$1.44 trillion and US$3,815 billion respectively. However, research by the KPMG Consulting illustrated that 59% of M&A performances were not good as expected. Many cases and statistics revealed that about 30% - 50% of the completed M&A in US failed, whereas the success rate did not reach 50% in the M&A cases in Europe. The cases showed that the performance of M&A would need to go through a conformity process to become effective. In this study, the case used was two apparel firms of different products in Hong Kong (Horizontal Merger), which for the reasons other than the above, agreed to merger to become one of the biggest apparel corporation in Hong Kong. Nevertheless, during the process of combination, many problems had arisen, such as: 1. Corporate Culture 2. Core Value 3. Measurement of Performance 4. Market Positioning 5. Organization Structure 6. Sales Operation 7. Operation Mode of Production 8. R&D Because of the differences in conceptual recognition, and changes in internal and external circumstances, the right and wrong attempts, in the course of learning process, had made from profits to loss, from loss to profits again and achieved a mixed effect in the growth path and future expectation. In this regard the operation was not smooth after the merger. But after continual improvement and re-engineering, the new company has become to make profit in 2004.