Intellectual Property Rights Law has long been known to protect the work or inventions created through thought processes. Protection is given to guarantee security in creating new things. Therefore, every intellectual property needs to be registered to avoid various violations of intellectual property. Trademark is one of the intellectual property that is widely used in the trade of goods and / services. Not a few famous brands imitated by those who want to take advantage in an easy and fast way. What's more famous brands that are not registered. The owner of a well-known mark will be severely disadvantaged if his mark is registered by a party who has bad faith. This study will discuss the protection of famous brands that have not been registered as seen from Law No. 20 of 2016 concerning Trademarks and Geographical Indications and the suitability of judges' decisions in deciding cases related to the Alstyle Trademark. In conducting research, the approach used is the legislative approach, case approach, and conceptual approach. From the research that has been done, it can be concluded that to get legal protection, a trademark must be registered first. If there is an objection, the trademark owner may file a claim against the trademark of the registered trademark based on the reasons contained in Article 20 and/or Article 21. In deciding the Alstyle Trademark case, the judge only considers the provisions regarding the trademark registration system in Indonesia and does not consider Article 21.