公司權益市值被高估時，經理人會不斷尋求增加短期利益之方法，以維持高估的股價。一旦市場發現公司表現無法達到預期時，公司股價可能快速、巨幅下跌，陷入財務危機甚至破產，公司長期價值將被徹底破壞。自Jensen（2004, 2005）提出高估權益市值之代理成本的觀點後，多篇文獻透過盈餘管理來間接推論高估權益市值確實會引發代理成本。與過去文獻不同的是，本研究嘗詴直接檢視高估權益市值與代理成本間之關聯性。研究樣本選自2001年至2007年間國內上市、櫃公司，進行實證分析。研究結果大抵支持權益市值高估可視為一項理想的代理成本變數。

Managers of companies with overvalued stocks often give the impression of achieving improved performance; however, their actions commonly sacrifice firm equity in the long run. The concept of agency costs of overvalued equity was first proposed by Jensen (2004, 2005), and since that time a number of studies have presented indirect evidence to support his claims. In contrast, this study tests Jensen's arguments directly, by examining the relationship between overvalued equity and agency costs. Data were collected on companies publicly traded on the Taiwan Stock Exchange and the Gre Tai Securities Market between 2001 and 2007. Multivariate regression analysis provided moderate support for our proposition that overvalued equity represents a further proxy of agency costs.