After the Asian financial crisis over the period of 1997-1998, M&A deals started to be active in Korean market. Around that period, back-door listing (or reverse takeover) was introduced in Korean market. Back-door listing means that a private company obtains an exchange listing through acquiring or merging with a public company. Since the requirements of initial public offerings are very strict in Korea, many companies have used back-door listings to obtain the public status since 2000. Before 2006, the regulation on back-door listing was not sufficient to maintain the soundness of back-door listing transactions. Back-door listing transaction caused many problems in capital markets because private companies involved in the transaction were not healthy in their financial structure and operational performance. In June, 2006, a new regulation on back-door listing was announced, and it forces private companies in back-door listing transactions to meet more strict requirements. After the new regulation was implemented, we could find some desirable back-door listing cases. This Celltrion case represents the positive function of a back-door listing. Celltrion is a biopharmaceutical manufacturing company. In the spring of 2002, VaxGen, a California-based biotechnology company, and a group of Korean partners founded what would be the largest biopharmaceutical contract manufacturer in Asia. Celltrion applied for IPO twice, but failed to obtain exchange listings due to the strict requirements of IPO. Then Celltrion tried back-door listing to acquire a public company’s status. Celltrion, a private firm, used a merger method - there are four different methods for back-door listing in Korea, such as merger, entire stock exchange, operation sales and swap - with ORchem which was a public company in Korea Securities Dealers Automated Quotation (KOSDAQ) market. After the transaction,Celltrion earned a cumulative abnormal return about 60% from day -3 to day +3 around the announcement of the transaction. A buy-and-hold abnormal return used to measure long-term performance was about 87% over the 12-month period after the transaction. The stock of Celltrion performed very well despite the financial crisis over the period of 2008-2009. The market value of Celltrion recorded two trillion won in 2009, which is the largest in KOSDAQ market.