在實務上，綠色關稅偏好（green tariff preferences）經常被用來解決貿易與 環境保護之間的爭端。本文欲分析進口關稅稅率與進口品的環保品質，二者彼此之間的相互變動關係。分析的結果顯示，稅率的降低是否足以促使廠商提昇進口品的環保品質，必須視環保品質的改善對消費者邊際效用的影響程度時，倘若改善進口品的環保品質得以減緩消費者邊際效用遞減的程度時，則降低關稅稅率可以提昇進口品的環保品質；而且，長期下的產品環保品質會較高。此外，本文也欲探究進口品的環保品質對一國政府制訂最適關稅政策的影響。一般而言，在人們缺乏環保意識的情況下，政府應採行高（低）環保品質進口品低（高）關稅稅率的最適關稅政策；而且，當產品環保品質的改善成本相對於其污染減量技術、或污染的邊際環境損害程度、或政府對環境品質的重視程度愈高時，則在長期下，對於高環保品質的進口品，政府應課以較短期時更低的關稅稅率。

　　　　　In practice, the green tariff preference concept has often been applied to settle trade disputes relating to environmental protection. This paper analyzes the correlation between import tariffs and the environmental quality of imports. We find that it is ambiguous whether a lower tariff leads to a higher environmental quality of imports since the existence of this phenomenon hinges on the effects of the environmental quality of imports on the marginal utility of the imports. Specifically, if the better environmental quality of imports can mitigate the decline in the marginal utility of the imports, then a lower tariff necessarily raises the environmental quality of the imports; moreover, the quality will be even higher in the long run. This paper also investigates, in a slightly different setting, the effect of the environmental quality of imports on optimal tariffs. In general, if consumers are not conscious of environmental protection, then the optimal tariff policy is to levy a high (low) tariff on imports with low (high) environmental standards.