This research aims to do and review the legal certainty from the crime of illegal fishing and factors that affect the weakness of law enforcement for foreign vessels that carry out unlawful Fishing in Indonesian marine areas. The type of research used in this research is normative legal research. Normative legal research is conducted by examining objects in the form of laws and regulations or legal norms that apply to a particular legal issue. The results showed that according to the International 1982 Maritime Law Convention (UNCLOS 1982), the enforcement of Illegal Fishing law had been regulated in Article 73 UNCLOS 1982, while in The Indonesian National Law has been handled in Article 69 Paragraph (4) of Law No. 45 of 2009 on Fisheries. Obstacles in legal certainty of illegal fishing include impenetrable law legal certainty, lack of seriousness and willingness of law enforcement, and lack of ethos and public awareness to play an active role in law enforcement of illegal fishing in the Indonesian marine territory.