This study aims to analyze the legal consequences of notarial deeds containing legal defects and to examine the forms of legal liability of a notary public regarding such defective deeds. The legal issues raised are the legal consequences of a legally defective notarial deed and the forms of legal liability of a notary for a deed containing legal defects. This study is a normative legal research employing a statute approach and a conceptual approach. The results indicate that a notarial deed containing legal defects can lead to two distinct legal consequences. First, it may be downgraded to a private deed (underhand deed) if it fails to fulfill the formal requirements stipulated in the Law on Notary Positions. Second, it becomes null and void by law (void ab initio) if it does not meet the material requirements under Article 1320 of the Indonesian Civil Code, particularly regarding a specific subject matter and a lawful cause. Consequently, the validity of a notarial deed is strictly determined by the fulfillment of both formal and material requirements during its drafting. Furthermore, the forms of legal liability imposed on a notary for a defective deed encompass civil, administrative, criminal, and ethical liabilities. Civil liability is grounded on tort or unlawful acts (Article 1365 of the Indonesian Civil Code), which may result in an obligation to pay damages, costs, and interest. Administrative liability manifests in oral warnings, written warnings, temporary suspension, or honorable/dishonorable discharge. Lastly, criminal liability may be enforced if criminal elements are met, including document forgery, alongside potential sanctions derived from the Notary Code of Ethics.