A well-known mark can implicitly be defined as a mark which has a high reputation and therefore, shall obtain a larger legal protection than that of a regular mark. Within Decision Number 57/Pdt.Sus-Merek/2014 /PN.Niaga.Jkt.Pst the Plaintiff wanted to register their mark in Indonesia under the category of wellknown marks, however, it was rejected by the Defendant by reason of being substantively similar to the Defendant’s mark. Considering this, the Plaintiff filed an appeal towards the Defendant but it was rejected by the Defendant, further, the Plaintiff filed a cassation to the Supreme Court and the Supreme Court issued Decision Number 329 K/Pdt.Sus-HKI/2015 which grants the Plaintiff’s claims as in full as well as declaring that the Plaintiff’s mark is a well-known mark. The purpose of this research is to understand the regulation of Well-Known marks in Indonesia and the legal consideration of the Supreme Court in issuing Decision Number 329 K/Pdt.Sus-HKI/2015. This research is a juridical normative research with a descriptive type of research. The approach conducted is the normative issue approach. The data being used are primary, secondary and tertiary data. The data collecting method is conducted through literature study and document study. Data processing is conducted by using qualitative data analysis in order to obtain objective truth. The result and discussion of this research are, firstly, that the Plaintiff falls under the category of well-known mark. Secondly, the Commercial Court was erroneous in interpreting the meaning of substantial similarity between the Plaintiff’s mark and the Defendant’s mark.