本文探討產品替代性和進口關稅，對廠商申請環保標章決策的影響；並討論環保標章制度是否必能降低農產品進口國之環境污染。本文所採之市場結構為：兩國廠商出口農產品至第三國，在第三國進行產量競爭。本文的結論如下：不對稱的環保標章決策造成產品差異化，可能同時增加取得及未取得環保標章廠商的利潤。即使申請環保標章的成本很低，Nash均衡結果也可能為不對稱的：亦即廠商可以策略性地藉由不對稱的環保標章決策，以增進彼此的利潤，如此仍有一家廠商出口非環保產品至農產品進口國；在此狀況下國內污染量容易上升。此外，非差別關稅之稅率變動，對申請環保標章的廠商家數、和進口國污染量，其效果可能為正也可能為負。

This paper studies the effects of product substitution and tariffs on eco-labeling decision. Whether or not the eco-labeling will reduce the total pollution of a country importing agricultural products is examined. The market structure is that two foreign firms export agricultural products to the domestic market and then engage in Cournot competition. Our major findings are as follows: Asymmetric eco-labeling decisions will generate product differentiation which may simultaneously increase both firms' profits. There still can be an asymmetric Nash equilibrium even when the eco-labeling cost is quite low. The total pollution of the importing country can easily go up with asymmetric eco-labeling decisions. Moreover, a increase in the non-discriminative tariff rate may increase or decrease the number of eco-labeled firms and the total pollution.