Nowadays Sulu Sea is becoming the core of geopolitics issues between Indonesia, Malaisya and the Philippines. The three countries are looking at Sulu Sea as the strategic environment which has the substance of their national security interest, but the maritime security condition at Sulu Sea has no longer stable after the existence of Abu Sayyaf Group.In this thesis will explain about the agreement of maritime security cooperation which is called as the Trilateral Cooperation Arrangement in preserving Indonesia, Malaisya and the Philippines national security interests at Sulu Sea. The agreement has been initiated by the minister of foreign affairs of those three countries in order to their common concern about the threat that has been conducted by the Abu Sayyaf Group.Indonesia, Malaysia, and the Philipinnes as the three countries who agreed in the Trilateral Cooperation Arrangement at Sulu Sea recognize the threat in the maritime areas is maritime piracy such as ship hijacking and kidnapping for ransom that could threatened their national security interest as well as their sovereignty at sea. Therefore in order to overcome the maritime piracy at Sulu Sea, the three countries implement the initiatives that have been agreed.