Due the developments of technology have caused trade from conventional systems to digital-based systems, namely online marketplace. The significant development of online marketplace can create a chance for some business actors to attempt a predatory pricing act and create unfair business competition among sellers on online market and offline market. The act of predatory pricing that is often found on online marketplace is in the form of large number of discounts in a long amount of time, with a purpose to get rid of the competing business actors and set an entry barrier for those actor businesses to get into the same market. Currently, there are no regulations specifically for predatory pricing on online marketplace on business competitors. This thesis will discuss on the regulations of predatory pricing in business competition law could catch up with the development of technology that have created a new type of market such as online marketplace. This study also discusses the regulations of flash sale on marketplace in view from predatory pricing regulations in business competition law. In this study, the author uses a normative judicial method with a statute approach and a conceptual approach. based on research compiled by the author, the predatory pricing regulations contained in Article 20 of Law Number 5 of 1999 are no longer able to keep up with digital developments which also encourage economic development, especially in Indonesia. In addition, more specific arrangements are needed for implementing flash sales in online marketplaces so that promotions with large discounts will not harm business competitors and set an entry barrier for new competitors.