This study aims to analyze the principle of Tabellionis Officium Fideliter Exercebo related to cyber notary. This principle states that a notary must work traditionally. The point is that a notary must work in a conventional way, namely making letters or deeds in real terms, not through the internet. This research is a descriptive research type of normative legal research. Normative legal research is research conducted by examining library materials or secondary data. Therefore, this study examines and analyzes the appropriate legal principles and theories to ensure legal certainty regarding the e-RUPS deed made by a Notary according to the Tablelionis Officium Fideliter Exercebo principle. The results of the study show that Cyber Notary cannot remove the duties of a notary who maintains the integrity of the product he produces as a complete piece of evidence. However, in order for an authentic electronic document containing an electronic signature to be used as evidence in a civil trial, it is not complete evidence and has evidentiary value, but is the same as an underhand deed. The biggest problem that arises is the debate about the validity of the deed made in the cybernotary system. There are also those who state that the cyber notary is contrary to the governing principle, or Tablelionis Officium Fideliter Exercebo, which means that the notary must act in a traditional way. In fact, cyber-notaries have existed since 1995, but have been hampered by the lack of an adequate legal basis.