The purpose of this research is to analyze: How is the implementation of MUI Fatwa No. 10 of 2008 concerning underhand marriage and the legal and social obstacles of underhand marriage in Padang Lawas Regency?, How can an interdisciplinary approach be used to understand and resolve family law problems that arise due to the practice of underhand marriage?, How is the analysis of Maqashid al-Syari'ah towards MUI Fatwa No. 10 of 2008 concerning underhand marriage?, How does an interdisciplinary approach contribute to strengthening the principles of Maqashid al-Syari'ah in the application of family law in Padang Lawas society? This research is a qualitative research with the type of field research. Qualitative research is used because it aims to understand social phenomena in depth related to the practice of underhand marriage and the implementation of MUI Fatwa No. 10 of 2008 in Padang Lawas Regency. This research was conducted in Padang Lawas Regency. Data collection techniques in this research are interviews, observations and documentation. The data analysis technique in this study uses a phenomenological model, with the following steps: Epoche (Bracketing), Phenomenological Reduction, Meaning Categorization (Meaning Units), Textural Description, Structural Description, Synthesis of Meaning and Essence. The results of this study can be concluded that the Implementation of MUI Fatwa No. 10 of 2008 concerning underhand marriage in Padang Lawas Regency has not been running optimally due to legal obstacles (not positively binding) and social obstacles such as low legal awareness, cultural factors, and the economic conditions of the community. The practice of underhand marriage still occurs because it is considered valid according to religion even though it does not have legal force. An interdisciplinary approach has proven effective in understanding and resolving this problem, because it integrates legal, religious, social, cultural, and economic aspects thoroughly. This approach is able to provide a more comprehensive solution than a single approach. In the perspective of maqāṣid al-syarī'ah, underhand marriage tends to be contrary to the objectives of sharia, especially in protecting offspring (hifẓ al-nasl), soul (hifẓ al-nafs), and property (hifẓ al-māl), because it has the potential to cause harm to women and children. An interdisciplinary approach contributes to strengthening the principles of maqāṣid al-syarī'ah through strengthening the law, increasing religious awareness, and social change in society, so that it can realize the benefit in family law