The article examines the problems of recognition of illegal decisions of subjects of power. The author draws attention to the fact that the decision of the subjects of power is a consequence of the implementation of the public-authority management function by the subjects of power. The legality of the decisions of the subjects of power is a necessary condition for the legality of activities to ensure citizens’ realization of their rights, freedoms and interests. The article states that the legality of the decisions of the subjects of power ensures the legality of administrative and regulatory activities, the proper level of law and order in the state, and the protection of the rights of participants in public-law relations. The author draws attention to the fact that administrative courts play a significant role in matters of legality verification, protecting rights, freedoms and interests by recognizing the decisions of subjects of authority as illegal. It is justified that the cancellation or invalidation of the decision of the subject of power can be considered one of the ways to ensure its legality and the extent of responsibility of the body or official who made the relevant decision. It is concluded that the annulment or invalidation of the decisions of the subjects of power, recognized by the court as illegal, is of undoubted importance for ensuring law and order by eliminating illegal regulatory and individual acts from the law enforcement mechanism, and restoring the violated rights, freedoms and legitimate interests of individuals in the field of public and legal relations. The article substantiates that recognition of an act as illegal is a separate way of protecting the violated rights, freedoms or interests of a person. If the act is recognized as illegal, the court, depending on the type of act, applies other methods of protection, annulment of the individual act, or invalidation of the normative legal act.