本研究採用Dhaliwal, Krull, Li, and Moser (2005)之實證模型研究投資相關稅負對企業權益資金成本的影響。Dhaliwal et al. (2005)利用股利所得與資本利得最高級距稅率計算股利稅租稅罰，然而，使用最高級距稅率計算而得知代理變數恐無法完全捕捉稅負對資金成本的影響，因此本研究參考許崇源、俞洪昭、洪盈斌與戚務君 （2000），假設在個人董監事等大股東之所得稅率較一般散戶為高的前提下，以個人董監事持股比例做為個人股東邊際稅率之替代變數，再計算股利稅租稅罰之代理變數。 本研究利用台灣經濟新報資料庫（簡稱TEJ資料庫）取得台灣上市櫃公司2000年至2009年之財務資料，進行迴歸分析。實證結果顯示，因股利所得稅率與證券交易所得稅率差異造成的股利稅租稅罰，會使得權益資金成本上升；而且因為機構投資人較一般投資人享有較多租稅優惠，造成其適用稅率較低；而公司的邊際投資人又多為機構投資人，因此機構投資人持股可減輕股利稅租稅罰造成權益資金成本上升的情形。 / This study uses the empirical model proposed by Dhaliwal, Krull, Li, and Moser (2005) to examine the effect of investment tax on the cost of equity capital. Dhaliwal et al. (2005) used the top statutory tax rates on dividends and capital gains to get the variable “penalty”; however, it may not perfectly capture the dividend tax penalty. We follow the assumption that individual directors and supervisors may adopt higher tax rate than other individual stockholders (Hsu, Yu, Hung, and ,Chi 2000), then derive the variable “penalty” by using the rate of shares owned by individual directors and supervisors as the proxy variable of individual stockholder‟s marginal tax rate. This study uses the financial data of listed companies in Taiwan via Taiwan Economic Journal database (TEJ database) from 2000 to 2009 for regression analysis. The empirical results show that the dividend tax penalty resulting from the difference between the tax rate on dividend and capital gain increase the cost of equity capital. Furthermore, institutional investors always receive more favorable tax treatment than individual investors, making them adopt lower tax rate, and a firm‟s marginal investor is more likely to be an institutional investor, therefore the aggregate institutional ownership mitigates the increase of cost of equity capital.