本文主要考慮一個包含本國中間財廠商、最終財廠商及外國最終財廠商，且最終財市場位於本國的垂直相關市場模型。其中外國最終財廠商可能採取外人直接投資的方式進入本國市場。本文關心的是本國若存有中間財市場會如何影響外國廠商進入前後的本國社會福利變化。 本文發現，當本國存在中間財市場時，本國最終財廠商可能因外國廠商進入而受益，不過中間財廠商卻可能因此蒙受損失。其次，若上、下游市場結構越接近獨占，則外國廠商進入本國市場越可能提升本國社會福利，此一結果明顯有別於當本國僅存在最終財市場時之情況。最後，若上、下游市場的競爭越趨激烈，則本國不僅歡迎較具生產效率的外國廠商進入，也可能歡迎較無生產效率的外國廠商進入，此一結果亦與過去未考量中間財市場存在的相關文獻所得之結果明顯不同。 ;This paper considers a vertical-related model with domestic upstream firms, domestic downstream firms, and one foreign downstream firm. We want to investigate how entry of the foreign firm will affect the domestic social welfare if the foreign firm adopts FDI into the domestic final good market. The three major findings of the paper are as follows: Firstly, when there is an intermediate good market in the domestic country, the foreign firm’s entry may be beneficial to the domestic downstream firm but harmful to the upstream firm. Secondly, if the upstream and downstream market structures are close to monopoly, then foreign firm’s entry may be beneficial to domestic social welfare. This result is quite different from the situation that there is no upstream market in the domestic country. Finally, if the upstream and downstream markets are more competitive, the domestic country welcomes not only the more efficient but also the less efficient foreign firm entry. This result is also quite different from the previous literatures that don’t take intermediate goods into consideration.