This study explores the legal implications of land transactions conducted without adhering to formal procedures in Indonesia, focusing on the sale and purchase of land ownership rights. Using a normative legal research method, the study examines Indonesian legislation, including Law No. 5 of 1960 on Basic Agrarian Principles (UUPA) and Government Regulation No. 24 of 1997 on Land Registration. It also analyzes Bantaeng District Court Case No. 3/Pdt.G/2023/PN Ban to understand the implications for third parties in land disputes.The research identifies a conflict between the substantive validity of informal agreements under the Civil Code and the formal requirements for land transfer stipulated by agrarian law. Informal transactions, often validated by mutual agreement and payment, lack the essential legal safeguards provided by registration. This creates significant vulnerabilities for third-party buyers who, despite acting in good faith, may face disputes arising from undocumented ownership claims. The absence of formal documentation undermines the legal certainty necessary for ensuring ownership rights.The case study illustrates how informal land transfers lead to conflicting claims, with third parties often caught in legal disputes due to non-compliance with formal procedures. While the principle of good faith offers limited protection, it does not override pre-existing ownership rights, even if established informally. This underscores the critical need for compliance with formalities to prevent disputes and secure ownership.The study concludes that strict adherence to formal land transfer procedures is essential for protecting all parties involved and ensuring legal certainty. It recommends increased public awareness of legal requirements and stricter enforcement of formal processes in land transactions. These measures are necessary to reduce disputes, protect third-party buyers, and establish a more reliable framework for land ownership in Indonesia.