This study discusses the reconstruction of online fiduciary security registration in Indonesia in order to improve legal certainty, digital efficiency, and accountability of public services. The online fiduciary registration system that has been implemented by the government has indeed succeeded in speeding up the administrative process and expanding access to services, but in practice there are still problems in the form of suboptimal regulatory harmonization, data validity, personal data protection, limited integration between agencies, and weak digital supervision mechanisms. This condition shows that administrative digitalization is not fully in line with the needs of modern legal certainty and governance. The formulation of this research problem includes: first, how effective the current online fiduciary registration system is in ensuring legal certainty for stakeholders; Second, what regulatory reforms are needed to improve efficiency and accountability in digital fiduciary registration. The research uses normative juridical methods with legislative, conceptual, comparative, and case approaches. The results of the study show that the online fiduciary registration system in Indonesia is quite effective administratively because it is able to speed up registration, reduce transaction costs, and increase access to national services. The system is not fully effective in ensuring legal certainty because there are still problems with system reliability, data accuracy, regulatory synchronization, information disclosure, and the power of electronic evidence when disputes occur. The theory of legal certainty asserts that an ideal system should have clear rules, consistent procedures, predictable outcomes, and equal protection for creditors, debtors, notaries, and third parties. The conclusion of this study emphasizes that the reconstruction of online fiduciary registration must be carried out comprehensively on aspects of legal substance, institutional structure, and legal culture. The ideal digital fiduciary registration system is not only electronic-based, but also ensures legal certainty, economic efficiency, data security, and fairness for all stakeholders. Thus, the renewal of the digital fiduciary system is a strategic need in national legal development in the era of digital economic transformation.