Abstract: With the rampant piracy， employing privately armed security guards on board against pirates attack has become more and more popular with shipping companies. Consequently， the basis of armed security guards use of force to combat pirates has been at issue. When an individual is confronted with an illegal attack， he or she is entitled to use force for self-defense， which is recognized by the customary international law and national laws. However， regarding the use of force for self-defense， there are no specific provisions in the maritime international law and there exist various versions of guidelines in the national laws， which make it difficult to provide privately armed security guards on board with clear and predictable laws and regulations in the use of force for self-defense. Therefore， in order to make better use of these effective measures to protect the shipping industry， the rules of force use for self-defense should achieve unity in the international level.

Key words: privately contracted armed security guard, piracy, self-defense