Upon the legalization of Law Number 1 of 1974 on Marriage, interfaith marriage is no longer applicable in Indonesia since marriage validity shall based on religious law. Most of those who are not able to perform an interfaith marriage in Indonesia get married overseas, despite it may be categorized as a form of legal smuggling as avoiding laws that supposedly apply to them. This study used conceptual, statutory, comparative, and philosophical approaches. Legal materials composed of normative primary, secondary, and tertiary legal materials were used in this study in such a way as observation, collection, and literature review as well as document, whether conventionally or via the internet. The results of this study suggested that interfaith marriage performed overseas by Indonesian Citizens is included as legal smuggling, and the legal certainty of law smuggling for interfaith marriage between Indonesian Citizens performed abroad only meets formal requirements which shall be valid under the law of the state where it is performed and does not meet material requirements namely Indonesian marriage laws in virtue of religious law.