本文以一高、低品質廠商雙占競爭的貿易模型，來探討貿易國政府片面開放市場或同時開放市場對廠商內生品質決策的影響。在Cournot數量競爭下，高品質生產國片面開放市場會使得產品品質全面提升，此時品質差異必會降低，但平均產品品質則有可能會降低，而高品質產品生產國的福利必會因片面開放而降低。若低品質生產國片面開放市場或兩國均開放市場，則低品質廠商的品質效率越好，有可能使全球福利反而降低。在Bertrand價格競爭下，高品質生產國片面開放市場，則低品質廠商的品質效率越差，會使高品質產品生產國的福利越低。在Cournot數量競爭下，兩國政府市場開放政策的Nash均衡為低品質產品生產國會選擇開放市場，高品質產品生產國則會選擇不開放市場。在Bertrand 價格競爭下，兩國政府市場開放政策的Nash均衡則為兩國均選擇開放市場。

This paper explores the firm’s endogenous quality choice in response to unilateral (or bilateral) market openness in a high/low quality firm duopolistic competition trade model.  Under Cournot quantity competition, a high quality country unilaterally opening its domestic market would (1) improve product quality generally, (2) narrow the quality differentiation between high/low quality countries, (3) probably decrease average product quality, and (4) deteriorate the welfare of the high quality country.  On the other hand, a low quality country unilaterally or two countries bilaterally opening the market would raise the low quality country is quality efficiency but possibly decrease global welfare.  Based on Bertrand price competition, a high quality country unilaterally opening the domestic market would worsen the quality efficiency of a low quality country and the welfare of the high quality country.  For Cournot competition, the Nash equilibrium of market openness policy is that the low quality country removes trade barriers and the high quality country keeps market closure.  However, the two countries would open their markets simultaneously under Bertrand competition.