有關城鄉失業的文獻，均在固定規模報酬的設定下，證得提高最低工資率會吸引過多的勞動人口移入，反而導致都會區失業率的上升。有別於於傳統城鄉失業模型文獻，本文從現實狀況出發，在新貿易理論之規模報酬遞增與不完全競爭的架構下，進一步考量廠商的異質性(大廠與小廠並存)，探討市場擴張與提高最低工資率，對廠商規模消長，以及失業率的影響。本文主要發現如下：由於大廠在邊際成本有較低的優勢，小廠優勢則在於較低的固定成本，(1)若產品替代彈性夠大，則具邊際成本優勢的大廠將受益於市場規模的擴大，而小廠則受害而減少；(2)在既定的替代彈性下，則提高最低工資抵銷了大廠的邊際成本優勢，導致其家數萎縮，而小廠數量則增加。最後，(3)有別於傳統城鄉失業文獻之提高最低工資，將導致都會區失業人口提高的結論，本文證得在大規模經濟與大小廠並存的設定下，提高都會區的最低工資水準，將可提高就業人口、降低失業率。

Most of the related literature on the rural-urban model, based on constant returns to scale and a perfect competition setup, proves that raising the minimum wage level will attract more migrants to an urban area’s modern sector and thus lead to a higher unemployment rate. Deviating from the traditional setup, we adopt the new trade theory of increasing returns to scale (IRTS) and imperfect competition, extend it to consider firm heterogeneity (the coexistence of big and small firms), and analyze how the market size and minimum wage level might affect the firm size distribution and the rate of unemployment in a small open economy. The major findings are as follows: With big firms’ advantage in marginal cost and small firms’ advantage in fixed cost, (1) if the substitution elasticity between the big vs. small firms’ products is large enough, then larger market size will benefit the big firms. (2) Given a level of substitution elasticity, raising the minimum wage will offset the big firms’ advantage in marginal cost. Thus, the number of big firms will decline and the small ones will increase. (3) Unlike the conventional results of increasing unemployment in a conventional rural-urban model, we prove that under IRTS with the coexistence of big vs. small firms, raising the minimum wage will increase the employment level and hence lower the rate of unemployment.