The legal consequences of the use of trademarks that have similarities at their core in Decision Number 55/Pdt.Sus-HKI/Trademark/2022/PN Niaga Jkt.Pst, as viewed through Law No. 20 of 2016 concerning Trademarks and Geographical Indications, were the subject of this study. The research conducted by the author was of a normative legal nature, using a literature review to explain the research findings with relevant literature. The approach used by the author was a legislative approach, particularly focusing on Law Number 20 of 2016 concerning Trademarks. The conclusion of this research is that the legal consequences of using trademarks that have similarities at their core, in this case, align with the plaintiff's claim, stating that the legitimate owner and user of the trademark in question is PT. Supra Usadhatama, and the registration of the trademark "PROVIT-C" under the name of PT. Mahakam Beta Farma should be rejected because it bears similarities at its core to the trademark "PRO-FIT."