國內、外有關合併購併的研究皆是針對非關係企業的水平合併、垂直合併或多角化合併。本文首度針對母公司將其子公司併入的事件，探討合併後的績效表現及宣告的市場反應。比較合併前後之合併報表，發現此類合併決策並無明顯的綜效產生。而投資人對此績效不彰的預期也反應在母公司的股價上，實証顯示合併子公司宣告會使母公司股價產生顯著為負的異常報酬，(-7,-1)期間之平均累積異常報酬(CAR)為-2.763%，(0,14)期間之平均CAR為-3.334%，顯示投資人認為母公司將子公司合併為一家法人可能為公司價值帶來負面損失。上述關於合併綜效和宣告效果的結論，皆與權益分割的相關研究相反。進一步檢視宣告效果之決定因素，發現「母公司合併前的營運績效較差」、「母、子公司非同屬相關產業」以及「母公司屬非電子業」會產生較為負面的宣告效果。此外，若宣告中提及此合併行為可改善財務透明度，反應會產生較為負面的宣告效果，此類宣示似乎反而讓投資人對母公司產一財務透明度方面的疑慮。最後，宣告後一年期間並未發現顯著的長期異常報酬。

Previous studies on merger and acquisitions (M&A) have been mostly focused on horizontal-, vertical-, or multi-M&A between unrelated enterprises. This is the first study to focus on the events of subsidiary merging by examining the merger synergy and the market response. We find no clear merger synergy, and investors predict that poor synergy will be reflected by the parent company’s stock prices. Second, we find negative abnormal returns on parent stocks from the announcements (-2.763% average CAR on event period (-7,-1) and 3.334% on period (0,14)), indicating that investors consider subsidiary merging to be a strategy pursued by the parent company to write off equity. This conclusion about merger synergy and announcement effects is in opposite to the results obtained from the related study concerning divesture. Third, more negative price impacts occur in events under the following conditions: a) when a parent company has poor previous performance, b) when the parent and subsidiary are in un-related industries, c) when the parent company is in a non-electronic industry, and d) when announcements of a merger action denote an improvement in financial transparency. Finally, we find no evidence of significant abnormal returns over a one-year- period after the announcement.