ABSTRACT ZULKHANADYA, 2020 Sophia Listriani, S.H., LL.M. Today, plastic waste is the most widely found in the Pacific Ocean, around 99% of garbage in the Pacific Ocean is plastic waste. Indonesia as the second-largest contributor plastic waste to sea, it needs to implement the state responsibility principle to fulfill the international obligations as referred to Article 235 (1) of the UNCLOS 1982 stated that states are responsible for the fulfillment of their international obligations concerning the protection and preservation of the marine environment. This study aims to explain the implementation of the state responsibility principle in Indonesia as a state that contributes plastic waste to the Pacific Ocean and to find out the challenges faced by Indonesia in implementing the State Responsibility Principle to handle the issue of plastic waste. This research is normative legal research. The data collected in this research is library research, by collecting, reading, studying, and understanding conventions, laws and regulations, textbooks, journals, and literature as well as data obtained from the internet that are relevant to the issues discussed. The results showed the implementation of state responsibility principle in Indonesia is applied through three legal instruments which are administrative law, civil law, and criminal law instruments. In reducing plastic waste, Indonesia's response has been well seen from Indonesian regulations and policies through the NPOA targets, but in implementing these targets the government is still weak. On the other hand, the challenges found because of the absence of special laws on marine plastic waste, waste management strategies have not been objective, lack of education, and public awareness on plastic waste. Strengthen government collaboration to realize Indonesia's NPOA target in reducing plastic waste. Revising the Presidential Regulation No.83 of 2018 on the Handling Marine Litter by adding clauses of management measures of marine plastic waste, and the settlement mechanism on plastic waste cases. Optimizing waste management strategies through the application of 3R (Reduce, reuse, recycle), issuing regulations on prices and mechanisms for the implementation of paid plastic bags, and creating a curriculum for environmental protection from plastic pollution in formal education.