Trademarks grown into an asset of its owner along with the development of the world economy. Trademark growth influenced the government to develop trademark laws to protect trademarks especially in Indonesia. Law Number 20 Year 2016 About Trademarks and Geographical Indications is the latest trademark law in Indonesia. In this thesis, writer want to explain the implementation of trademark law in Indonesia especially the protection of well-known marks. In this thesis, writer use a type of normative juridicial research that based on the living legals norm in Indonesia. To collect data in this thesis, writer uses library study as a method to collect data. This thesis uses qualitative data analysis techniques that based on case approach that is based on the cancellation of NOVEC 1230 case and statute approach based on the trademark law in Indonesia. This thesis want to explore and analyze the cancellation of NOVEC 1230 trademark that is owned by Dewi Nilasari. NOVEC 1230 violated the similarity in principle rule with NOVEC trademark that is owned by 3M Company. Besides violating the similarity in principle rule, Dewi Nilasari also registering NOVEC 1230 trademark on the basis of bad faith. Accordingly, the Commercial Court’s Decision and Cassation Decision decide to cancel the NOVEC 1230 trademark registration, stated that NOVEC 1230 trademark registered on the basis of bad faith, and stated that NOVEC trademark is a well-known marks. Based on the analyisis in this thesis, writer agrees with the Commercial Court’s Decision as well as Cassation Decision. Writer came to the conclusion that Dewi Nilasari violates the similarity in principle rule and registering NOVEC 1230 trademark on the basis of bad faith. Writer suggest the Intellectual Property Directorate General to tighten the substantive examination of a trademark registration and adding implementation rules of the protection of well-known marks.