This study examines the responsibility of states for human rights violations by private security companies in foreign missions. The present study shows that despite significant theoretical advances, the international legal system faces numerous implementation challenges in the field of monitoring and accountability of these companies in practice. By present analyzing three levels of state responsibility, including responsibility arising from operational control, responsibility based on the lack of effective monitoring, and guaranteed responsibility, the study provides a comprehensive framework for understanding the obligations of states. The  findings indicate that existing international instruments, including the Montreux Document and the UN Guidelines, despite their theoretical value, have limited effectiveness due to the lack of adequate implementation guarantees. On the other hand, international jurisprudence, although it contains valuable principles, requires greater coherence due to its fragmentation and differences in standards. The identification of deep gaps in the current system, including lack of contractual transparency, conflict of laws, and weak oversight mechanisms, are other important findings of this research. By providing practical solutions at the international and national levels, including proposing the development of a comprehensive treaty, amending domestic laws, and strengthening judicial cooperation, this article proposes effective steps to strengthen the accountability system. This research ultimately emphasizes that the issue of state responsibility towards private security companies is an important test for measuring the effectiveness of the international human rights system in the face of new developments in the field of global security.