本文主要的目的在於設立一個產業內直接外人投資的理論模型並以美國在1983年到1990年間十九大製造業的資料作實證分析,以探討產業內直接外人投資的決定因素。實證結果顯示:美國的貿易障礙、市場規模、工會團體與世界其他國家的貿易障礙等因素對美國製造業之產業內直接外人投資有顯著性的影響。然而,世界其他國家的市場規模,美國與世界其他國家之勞動生產力比,產品差異程度與多國籍廠商之特定優勢等因素對美國製造業之產業內直接外人投資沒有顯著性的影響。 The purpose of this paper is to build a theoretical model of intra-industry direct foreign investment (IIDFI) that can be empirically implemented to explore the determinants of IIDFI between the U.S. and the rest of the world in manufacturing industries from 1983 to 1990. The evidence presented in the study shows that trade barriers, market size and labor unions in the U.S. and trade barriers in the rest of the world have significant effects on IIDFI; however, market size in the rest of the world, U.S. productivity (to the rest of the world), product differentiation, and foreign multinational firm-specific advantages seem to have insignificant effects on IIDFI.