The purpose of this paper is to clarify the present state and problems of Japanese measures against the protection and preservation of the marine environment from the perspective of international law and Japanese domestic laws and regulations. The analysis is divided into three sections. Firstly, the relationship between Part XII of UNCLOS and the IMO marine environmental treaties will be addressed in brief. Secondly, Japanese implementation of the IMO treaties will be addressed in the context of the regulations regarding both dumping waste into the sea from vessels and marine pollution from vessels. Finally, this paper will clarify the problems regarding the Japanese implementation of marine environmental treaties.