本文利用垂直產品差異化模型，探討經濟整合對不同品質產品生產國家福利的影響，以及品質差異程度在經濟整合過程中的重要性。在貿易成本的設定上我們同時考慮文獻上會用的二種型式：運費和關稅。本文發現，這二種設定的經濟整合福利效果差異甚大。在運費型式之下，無論兩國產品品質差異為何，低品質國家在經濟整合過程中必定受益；而高品質國家在品質差異程度不為大時，整合過程可能會出現福利先下降再上升的情況。此隱含在經濟整合過程中，對低品質國家有利時對高品質國家未必有利；但只要是對高品質國家有利則低品質國家也一定受惠。相反地，在關稅設定下，不論不用品質產品生產國的進口關稅稅率為相等或不等，在經濟整合過程中，遭逢傷害的則為低品質產品生產國；高品質國家的福利水準反而是隨著關稅下降持續地上升。顯示關稅型式的經濟整合在二國之間產生了利益衝突，經濟整合不易實行。

This paper constructs a vertical intra-industry trade (VIIT) model to explore the welfare effects of economic integration with different quality products as well as the role of the degree of quality differentiation. We take into account both popular settings of trade costs in the literature-transport costs and tariffs-and find that there is a significant diversity in welfare efficacy. In the transport costs setting, no matter what the product quality differences are, the low quality country will be better off as economic integration proceeds. However, the high quality country might be better off or worse off during the process of economic integration, depending on the degree of quality differentiation. This implies that what is good for the high quality country also benefits the low quality country, but the opposite is not always true. Contrarily, in the tariffs setting, a drop in trade costs definitely benefits the high quality country, while it may harm the low quality country. This shows that a tariff reduction gives rise to a conflict between the two countries, and economic integration is not always an easy road to travel on.