This study analyzed merger announcement effect using case study method after selecting 302 merger data of stock-listed corporations that made merger announcement with the Financial Supervisory Service between July 2006 and June 2012 as primary samples and classifying them into reverse mergers and general mergers. As a result of measuring and analyzing the abnormal returns before and after the announcement of merger, in both the reverse merger and the general merger, the existence of merger announcement effect and the establishment of semi-strong form efficient market hypothesis were verified. Especially in the case of reverse merger, the efficiency of the announcement was found to be a little improved after the global financial crisis. Among primary samples, 181 merger data for which elementary statistical data can be obtained on major variables related to merger were selected as secondary samples. Analysis of variance(ANOVA) and multiple regression analysis were performed on the effects of the types of the merger and the financial characteristics of merging and merged firms on the cumulative abnormal return. Here, secondary samples were divided into the merger samples that are not backdoor listing, the reverse merger samples, and the cases in which the merger price of the stock-unlisted merged corporation differed from the intrinsic value appraised by an outside appraisal organization announced on the registration statement(merger). Summarizing the results of ANOVA and regression analysis, in the merger samples that are not backdoor listing, the merging firm’s market value scale variable had a significant negative(-) effect on the cumulative abnormal return, and the merging firm’s growth rate of sales variable had a significant positive(+) effect, and the merging firm’s share percentage held by the largest shareholder variable particularly had a significant positive(+) effect with relatively largest importance. This probably suggests that, in the merger samples that are not backdoor listing, the merging firm’s share percentage held by the largest shareholder has greater positive announcement effect on the market. In the reverse merger samples, the diversifying dummy variable had a significant positive(+) effect, and the affiliated dummy variable had a significant negative(-) effect on the cumulative abnormal return. In the cases of reverse mergers, the increase of the possibility for investment recovery for the existing shareholders of the listed merging firm due to the increase of the number of shares in the market and the transaction amount after the success of the merger is judged to have a positive effect on the increase of the wealth of the shareholders of the merging firm before and after the merger announcement. In cases of merger between a stock-listed corporation and a stock-unlisted corporation, a difference occurs between the merger price and the intrinsic value if the merger price of the stock-unlisted corporation is not the intrinsic value appraised by an outside appraisal organization, and this difference is called the merger premium in this study, and as a result of analyzing whether it has a significant effect on the cumulative abnormal return in the existing multiple regression analysis model, it did not had a significant effect.