This study examines the legality of Minister of Home Affairs Decree No. 300.2.2‑2138 of 2025, which administratively transferred four islands from Aceh Singkil Regency (Aceh Province) to Central Tapanuli Regency (North Sumatra Province). The research focuses on assessing the decree’s compliance with key principles of administrative law, particularly legality, normative hierarchy, and administrative justice in territorial governance. Employing a normative approach and document analysis method, the study finds that the ministerial decision potentially exceeds administrative authority, as it was not based on a statutory revision or government regulation and lacked consultation with affected local governments and communities. These findings highlight the urgent need to strengthen legal oversight over strategic administrative acts to safeguard regional autonomy and jurisdictional certainty. The study recommends judicial review through the Administrative Court and calls for a comprehensive reform of inter-agency coordination mechanisms in resolving inter-provincial boundary disputes