Trademarks are the most essential and valuable aspects of the trade sector. As part of Intellectual Property Rights, a brand functions as the distinguishing power of a product and the identity of the company. The more well-known a brand is in the community, the more likely it has unfair business competition by using/imitating a brand that is similar in principle to a well-known brand. The owners of a brand have the right to prohibit other people from using the same brand or having similarities with their brands by filing a lawsuit for the cancellation of an application for registration of a similar brand if it is proven to have bad faith. Based on the description above, the author intended to describe the application of trademark law in Indonesia, particularly the protection of well-known brands based on international regulations and Law number 20 of 2016 concerning Trademarks and Geographical Indications. Besides, the author also analyzed the legal considerations used by the panel of judges in deciding cases of similarity in principle with a well-known brand in the decision number 37/Pdt.Sus-Merek/2019/Pn.Niaga.Jkt.Pst using the normative juridical approach. The data used in this study were primary, secondary, and tertiary data. Data collection was performed by a literature study and document study.