關於國際私法上子女身分之準據法，民國99年修法前的舊涉民法第16條及新法第51條分別設有選法規定。於修法前，我國學說對於子女身分準據法的規範意旨，見解並不一致。此點爭執於民國42年制定涉民法前即已存在，甚至在民國99年的修法過程中，各修正草案對於子女身分準據法的規範意旨亦表現出不同的理解方式。因此，本文擬先從比較日本法的觀點探討舊涉民法對於子女身分準據法的規範意旨，並觀察民國99年涉民法的修法過程，以分析新舊法間的根本差異為何。新涉民法第51條主要為儘量保護子女婚生性，採用子女、母或母之夫之本國法的選擇適用主義，其連繫方法遠比舊法複雜，難免發生不少解釋論上的難題。本文從比較日本法、德國法的觀點，分別探討涉外婚生否認的處理方式、子女本國法的確定方法及其特性、以及相關條文間的適用順序等具體問題，其中，除解明新法第51條的具體適用方式外，亦分析該條規定的利弊得失，並指出在立法論上有待商榷之處。

On the applicable law to child’s legitimacy, Article 51 (or Article 16 before the reform in 2010) of ＂Act Governing the Choice of Law in Civil Matters Involving Foreign Elements＂ provides choice of law rule. Before the reform in 2010, there was a dispute on the normative intent of this article. This dispute had already existed prior to the enactment of the Act in 1953. Furthermore, in the drafting process of the reform in 2010, each different draft had shown different understanding on the normative intent of the applicable law to child’s legitimacy. In order to understand the fundamental difference between the past and present law, this study will first analyze the normative intent of the past law from the comparative perspective with Japanese law. On this basis, the drafting process in the reform will be further examined. In order to protect the child’s legitimacy as broadly as possible, the new Article 51 adopted the alternative application method among the national law of child, its mother and husband of child’s mother. This choice of law method is much more complicated than that of the past, which would arise more difficulties in its interpretation. Therefore, this study will further analyze the concrete choice of law process under the new provision, focusing on following issues: how to apply this provision to the impugnation of legitimacy; how to determine the national law of child; the characteristics of the national law of child; the order in applying the related provisions. Through this concrete examination, this study will clarify merits and demerits of the present law.