本研究的研究目的在於探討董監事持股質押的代理問題對會計資訊與股票報酬相關性之影響，以驗證質押所引發的代理問題會降低公司盈餘資訊與股價報酬的相關性。 研究結果發現，當公司董監事持股質押比率愈高，公司盈餘資訊與股價變動的相關性愈低。由於董監事持股質押加深控制股東與外部股東之間的代理問題，造成當期盈餘對未來經營績效的預測力下降，加上盈餘管理的誘因增強，降低財務報導的可信度，都會造成盈餘資訊與股票報酬的相關性降低。 其次，本研究也發現董監事持股質押對盈餘資訊與股票報酬相關性的弱化效果，在虧損公司及股價表現不住公司會較嚴重。當公司處於虧損狀態時或股價表現不佳時，公司股價較容易出現下跌壓力，使得擁有管理控制權之董監事，因為個人財務困難而剝奪公司資產以及盈餘管理的可能性增加，因此即使公司當期盈餘有好消息，市場也會因為潛在代理問題較嚴重，而降低對盈餘好消息的反應。 實證結果也發現董監事持股質押對盈餘資訊與股價報酬相關性的弱化效果，在非電子類股會較電子類股嚴重。台灣電子類股產品競爭性強，需要專業團隊，其法人股東大都不是來自同一家族企業，因此法人股東之間可以相互監督，董事會的監督功能也較強，因此潛在的代理問題較輕。這種來自監督機制所帶來的利益會降低董監事持股質押對盈餘資訊與股票報酬相關性的弱化效果。

The purpose of this paper is to examine the effect of the agency problem due to collateralized shares on the relation between accounting earnings and stock prices. The empirical results show that the higher the extent of shares as collateral by the board of directors, the weaker the relation between the accounting earnings and stock prices. Collateralized shares will reinforce the agency problem between controlling shareholders and outside shareholders leading to lower prediction power of current earnings on future earnings. Furthermore, shares as collateral by the board of directors raise the incentives of earnings management. Earnings management will reduce the credibility of accounting numbers and thus will mitigate the relation between accounting earnings and stock returns. Moreover, we also find that the effect of collateralized shares on the relation between accounting earnings and stock prices is even weaker for the firm experiencing losses or for the firms experiencing stock price decline. When firm experience losses or stock price decline, the managers might have higher incentives to expropriate outsider shareholders or to engage in earnings management. Hence, the stock market might not positively response to good news in earnings because of severe agency problems. The effect of collateralized stock on the relation between accounting earnings and stock prices is also weaker for the non-electronic firms than for the electronic firms. Electronic firms typically face strong product competition and need professional supports. Under this scenario, institutional investors are generally not from the same family and can monitor one another more efficiently. Thus, monitoring from the board is stronger for the electronic firms and leads to less severe agency problems. The monitoring from the board lessens the adverse effect of shares as collateral by board of directors on price-earnings relation.