The performance of flats, especially commercial flats nowadays is no longer only to fulfill the need for a place to live but has also become a form of fulfilling modern life. The high public interest in flats has provided great opportunities for developers to increasingly build and sell their property products. One of the sales techniques that are often used by developers is the pre-project selling system. In this system, the marketing and sales of apartment units are done by the developer before the construction of the flat is built or is still under construction. Unfortunately, the legal regulations regarding marketing and sales in the pre-project selling system are still lacking in Law of the Republic of Indonesia Number 20 of 2011 concerning Flats (UU Rusun). Therefore, the problem formulations to be examined in this research are how the marketing of the Menara Jakarta apartment in the pre-project selling system is reviewed from UU Rusun and how is the legal protection for the consumers based on the order letter that used in the pre-project selling system of Menara Jakarta in case the developer was default based on the Supreme Court's Decision Number 3020 K / PDT / 2019. The purpose of this research is to analyze how UU Rusun provides legal protection for consumers in marketing and sales using order letters in the pre-project selling system. This research is a normative legal research with an approach to the systematics of law and case law. The data analysis technique used is qualitative analysis of secondary data that has been collected through the literature study. Based on the research that has been done, it can be known that the performance of marketing in the pre-project selling system is basically allowed by UU Rusun, as long as the developer meets the specified marketing requirements. Unfortunately, UU Rusun does not regulate legal sanctions for violating the marketing requirements, which makes developers even more willing to violate these provisions. Meanwhile, legal protection related to sales using an order letter based on UU Rusun and its implementing regulations is very weak, as a result of legal loophole related to sales made before the construction of flats was built and the non-existence of legal regulations itself regarding the order letter in UU Rusun. The conclusion from this research is that the legal protection provided by UU Rusun on marketing and sales in the pre-project selling system is still very weak in protecting consumer interests.