本文建屯一個三國二要素模型，討論本因素進口與產品出口之最適貿易政策。在模型中本國由外進口一獨佔生產因素配合國內之另一生產因素，生產產品並將此一產品全圓輸出至第三國。一般而言，當因素莖求曲線不是很凸向原點時，本政府的最適關稅政策是對進口因素課稅以矯正進口因素獨佔所造成之扭曲。本國政府也可以對出口品課稅（當進口因素為正常生產因素時）或補貼（當進口中間財為一劣等生產因心時），來減少外國獨佔廠商之剝削。有趣的是，本文證明此兩種政策可完全替代，二者皆能導致相同的產量與福利水準。

　　　　　We establish a three-country two-factor model to compare the optimal factor import policy with the optimal output export policy. In the model, there is a home country importing a factor from a foreign monopoly market, combining it with a domestic factor to produce a final product to be entirely exported to a third country. If the import demand for the factor is not too convex, the home country should impose a positive tariff on the factor import so as to diminish monopoly distortion. An export policy on the output serves also to diminish the distortion. In the case, the home government should tax (subsidize) the export if the importing factor is a normal (inferior) factor. Domestic welfare and output are the same under the two policies.