本研究探討我國實施兩稅合一制及兩稅合一制下施行最低稅負制及調降營利事業所得稅率對於上市櫃公司外資股權比例之影響。本文的實證結果顯示，兩稅合一制實施後，上市櫃公司稅額扣抵比率愈高者，其外資持股比率下降愈多，符合租稅顧客效果假說。此外，兩稅合一制下施行最低稅負制後，加徵最低稅負之上市櫃公司，其外資股東之持股比率減少與最低稅負加徵之稅額有顯著之正向關係。最後，兩稅合一制下調降營利事業所得稅率後，有效稅率降低之上市櫃公司，其外資股東之持股比率顯著增加。本文的研究發現延伸租稅顧客效果之研究，提供股東的租稅顧客效果於兩稅合一稅制下之實證證據，亦有助於了解兩稅合一制下公司稅制租稅變革的實質稅負效果。

This study examines the effects of imputation systems and tax reforms under the imputation system on foreign ownership of Taiwanese listed firms. As the tax clientele theory predicted, the results show that after the implementation of imputation systems in 1998, Taiwanese firms with higher imputation credit tend to have a lower percentage of foreign ownership, ceteris paribus. Further, after adopting the alternative minimum tax in 2006, firms paying the higher alternative minimum tax tend to have a lower percentage of foreign ownership. Finally, after reducing the corporate income tax rate in 2010, firms with a decreased effective tax rate tend to have a greater percentage of foreign ownership. Our study extends prior research by providing empirical evidence on the tax clientele theory under an imputation system and contributes to the understanding of the substantive effects of corporate tax reforms under such an imputation system.