This study discusses characteristics and regulations of assembly and demonstration on the Sea. One of the characteristics of assembly and demonstration on the sea is danger caused by vessels and nature of the sea. Thus, Korea Coast Guard prefers to regulate demonstration on the sea more strictly by applying sea related laws such as Maritime Safety Act and Public Order in Open Ports Act. However, assembly and demonstration on the sea is one of the fundamental rights which is guaranteed by the Constitution and should be regulated and protected by the Assembly and Demonstrations Law. The purpose of this article is to properly regulate and protect assembly and demonstration on the Sea based on proper interpretation of the Assembly and Demonstrations Law.