At the end of 2008, the European Union launched EU NAVFOR's anti-piracy operation which is part of the defense and security security policy (CSDP) as a military preventive measure aimed at addressing the problem of Somali piracy that is rampant in the Gulf of Aden maritime traffic lane. The background of this research is based on the success achieved by the EU NAVFOR operation in overcoming Somali piracy. The problem formulation in this study is why EU NAVFOR's anti-piracy operation is effective in overcoming Somali piracy. The main focus of this research is to analyze the factors that support the effectiveness of EU NAVFOR's operations carried out by the European Union through various policy instruments and the development of cooperation with various other international actors in overcoming the problems of Somali piracy during the period of 2008 to 2014. Knowing this, researchers use the regime's effectiveness theory and relate it to the concept of collective security cooperation as a framework of thought. This framework relates to the institutional capability and typology of the problems faced and the security cooperation built. Through this framework, results were obtained that the implementation of the EU NAVFOR operation proved effective in overcoming Somali piracy with indicators of declining piracy cases and achieving operational mandates, as well as stability in security conditions in the Gulf of Aden which began to be conducive.