Based on the recent changes in the concepts of ”Family” and ”Marriage”, this article focuses on the legal conditions of 1999 French ”PACS” (registered partnership) contract and its legal effects, on comparison with the Belgian and German Family Laws. It figures out the possibilities for guaranties to the same-sex/ different-sex registered partnership in Family Law, beyond the traditional heterosexual marriage. In addition, this article demonstrates the importance to respect the ”vested rights” acknowledged by the national Family Laws, in the theory and practice in International Private Law. Finally, it urges that the Taiwanese Family Law and the Internal Private Law as well need some revision to adapt to these changes in the social reality.