過去對公司資本結構的研究可分為兩大方向，一是對資本結構理論的探討，一是對影響公司資本結構因素的探討。我國於87年對投資所得改採兩稅合一制度後，兩稅合一對公司資本結構影響的探討成為研究的主流。本研究所要探討的問題有三。第一，兩稅合一後，公司的負債融資比例是否下降；第二，兩稅合一後，有效稅率、現金股給付率和獲利率與負債比率間的交互作用情況為何；第三，不同有效稅率或公司規模對負債比率的影響。 本研究的實證結果如下： （一）兩稅合一後，公司的負債比率會下降。 （二）兩稅合一前後，有效稅率與負債比率均呈正向關係；而且兩稅合一 後，有效稅率對負債比率的影響下降。 （三）兩稅合一前後，現金股利給付率與負債比率均呈反向關係；而且兩 稅合一後，現金股利給付率對負債比率的影響下降。 （四）兩稅合一前後，獲利率和負債比率均呈反向關係；而且兩稅合一 後，獲利率對負債比率的影響上升。 （五）兩稅合一之後，原有效稅率較高之公司的負債比率下降程度較多， 而原有效稅率較低之公司的負債比率下降程度較少。 （六）兩稅合一之後，原規模較大之公司的負債比率下降程度較少，而原 規模較小之公司的負債比率下降程度較多。 / The past researches on corporate financing structure can be divided into two lines, one in the corporate financing theories and the other in the determinants of corporate financing decisions. After the tax integration, the research whether the adoption of tax integration has a significant impact on corporate financing structure have become a mainstream. The study investigates three issues. The first is to investigate whether the debt ratio decreases after tax integration. The second is to investigate the effect of effective tax ratio, dividend payout ratio, profitability on the debt ratio. The third is to investigate whether the effect of tax regime change on the debt ratio is difference between effective tax ratio and firm size. The empirical results show follows: (1) After tax integration, the firm’s debt ratio decreased. (2) Effective tax ratio has positive relation with debt ratio no matter before or after tax integration. After tax integration, the degree of effective tax ratio effect on debt ratio declined. (3) Dividend payout ratio has negative relation with debt ratio no matter before or after tax integration. After tax integration, the degree of dividend payout ratio effect on debt ratio declined. (4) Profit ratio has negative relation with debt ratio no matter before or after tax integration. After tax integration, the degree of profit ratio effect on debt ratio increased. (5) After tax integration, the decline of debt ratio for company with higher debt ratio is more than the decline of debt ratio for company with lower debt ratio. (6) After tax integration, the decline of debt ratio for small firms is more than the decline of debt ratio for large firms.