外人直接投資經常被視為一個國家經貿自由化與國際競爭力的指標，在當代多邊貿易規則建立以及區域經濟整合兩股潮流的交互影響下，開放國內市場並引進外人投資已成為許多國家的重要政策。然而，外人投資的引進雖可以增加地主國經濟發展，但亦可能造成國內產業的負面影響，尤其在外資併購國內企業的情況下，更容易引起地主國之疑慮。因此，在強調貿易與投資自由化的同時，各國亦建立起對外人投資併購的「國家安全審查程序」作為外資進入本國市場的安全閥。目前主要的國際公約與國際經濟組織都未對「跨境投資審查」作出一致性規範，使得各國在審核外人投資的程序上有很大的自主性。「國家安全」最常被認為是保護地主國國內經濟文化、敏感產業、環保勞工等議題的重要手段，也正因為「國家安全」屬於不確定之法律概念，比較與觀察超國界法實踐遂成為重要課題。本文研究範圍聚焦於外資併購類型中之「國家安全審查」機制運作與法理，同時進一步以案例分析研究法，探討各國在面臨外資併購時，如何兼顧「投資自由化」與「國家安全保障」，並提出我國應提高投資審議委員會組織層級、針對國營企業跨境投資併購加以事前審核、以及強化國家安全審查機制透明化等修法與政策建議。

Foreign Direct Investment (FDI) is a popular index for evaluating the liberalization of trade and economic as well as national competitiveness of a country. Resulting from the effects of establishing the multilateral rules and regional economic integration in the modern world, opening the domestic market and encouraging foreign investment become the most important trade policy for various countries. However, although foreign investment increases the economic growth of home country, it may causes the negative effects for domestic industry at the same time. Especially in case of cross-border merger & acquisition, it brings more and more concerns from the home country. For above reasons, many countries use “national security review process” as a safeguard for the liberalization of trade and investment. Recently, most critical international agreements as well as international economic organizations are silence on the consistence regulatory of “cross-border investment review process”, and it makes more autonomy for every country to conduct her own foreign investment review mechanism. Moreover, “national security review” becomes a critical approach for protecting domestic economic, culture, sensitive industries, environment, and labor standard. Since “national security” is an undefined terminology for universal legal practice, compares and observes transnational state practice is a useful tool for policy making. The scope of this article focus on “national security review” process and its legal basis on the cases of M & A foreign investment type. This article also explores how certain countries balancing between “liberalization of foreign investment” and “protection of national security”. Under comparative legal method, this article examines the regulations of Australia, Canada, EU, and U.S.A. by some famous cases of state-owned enterprise (SOE) of Mainland China, which is the fastest and biggest M & A foreign investment around the world. In the end, this article provides conclusion and suggestion for Taiwan’s future improvement amendment for investment regulations, including considers higher level of Investment Commission, uses pre-entry review process for any cross-border government investor, and enhances the transparency of national security review process etc.