本研究以2004年至2010年在台灣申請首次公開發行(Initial Public Offering, IPO)的公司之競爭對手公司為樣本，分析IPO事件對同產業競爭對手公司的影響。首先以事件研究法檢驗IPO事件對同產業競爭對手公司短期股價報酬的影響，結果發現IPO成功完成事件對同產業競爭對手公司造成負向股價反應，而IPO失敗撤銷事件相反地造成正向股價反應。接著以單變數檢定分析IPO成功完成事件前後下，同產業競爭對手公司之營運績效是否有顯著差異，結果發現IPO後的營運績效顯著變差。最後panel迴歸分析結果也指出IPO成功完成事件確實對同產業競爭對手公司之營運績效造成惡化的結果，其ROA及ROE分別顯著下跌0.714%及2.675%的幅度。綜合以上實證結果，可以看出同產業競爭對手公司因IPO公司相對競爭優勢提升而造成績效表現不佳的現象。 This study analyzes the effect of initial public offerings (IPOs) on competitors in the same industry. The sample is composed of IPOs and their industry rivals in Taiwan from 2004 to 2010. First, we use the event study method to examine the effect of IPOs on short-run stock prices and returns of rivals, and the result shows that rivals experience negative stock price and return reactions to completed IPOs in their industries, and positive stock and return reactions to the withdrawals of IPO. Next, we examine the difference between pre-IPO and post-IPO operating performance of rivals. The result shows that the performance of rivals is significantly lower after IPO completed events. Finally, the result of panel regressions also show that significant deterioration in incumbent firms’ operating performance; ROA and ROE decline by a statistically significant 0.714% and 2.675% in IPO years. Overall, because of the better competitive advantage of IPO firms, the industry competitors’ performance deteriorate.