The author of the article substantiates the relevance and timeliness of the systematization of the subjects of national security and defense of Ukraine. On the basis of generalization and analysis of the current legislation in the field of national security and defense, the author has defined the system of subjects of national security and defense of Ukraine as follows: 1) management subsystem (the President of Ukraine); 2) controlled subsystem: security forces – law enforcement and intelligence agencies, state agencies of special purpose with law enforcement functions, civil defence forces and other agencies; Defense Forces – the Armed Forces of Ukraine, as well as other military formations, law enforcement and intelligence agencies, special purpose agencies with law enforcement functions formed in accordance with the laws of Ukraine; defense-industrial complex; citizens and public associations; 3) auxiliary parts of the system (Verkhovna Rada of Ukraine, Cabinet of Ministers of Ukraine, judicial agencies, international institutions). It has been offered to amend Part 1 of the Art. 12 of the Law of Ukraine “On National Security of Ukraine”, supplementing the four interconnected components of the security and defense sector with a fifth one – leadership in the field of national security and defense. At the end of the list contained in Part 2 of the Art. 12 of the Law of Ukraine “On National Security of Ukraine”, we consider it necessary to add the phrase “and other authorized agencies”, since the existing list of agencies that are part of the security and defense sector is not exhaustive. The main subjects of national security and defense of Ukraine have been characterized.