The purpose of the work is to establish the methodological foundations of the study of the essence of the category «administrative act». In the course of the research it was established that the methodological component is a set of research methods by which science achieves its fundamental goal - the acquisition and formation of new knowledge about the studied phenomena and processes. It is emphasized that the arsenal of scientific methods used in administrative law is extremely wide and includes both empirical methods - measure ment, observation, comparison - and purely theoretical. It was found that the administrative act, being the main form of activity of public authorities, is the basic, central concept of the science of administrative law; which is correlated with many other administrative and legal categories (administrative procedure, public-power relations, etc.). Based on the presence of polysemantic research links of the studied category with other administrative and legal institutions, the difficulty of choosing the appropriate methodological basis is emphasized, which requires a comprehensive approach to the choice of scientific tools of various theoretical constructions. Taking into account the established tradition in administrative and legal research, the expediency of using a three-level methodological model of scientific knowledge of the essence of the concept of administrative act, consisting of philosophical, general and special legal levels. It is concluded that the high heuristic potential of dialectical and systemic approaches is characterized by the possibility of considering the system of administrative law, which is an administrative act, on several levels: as a subsystem of society, as a component of modern law, as a separate system. It is emphasized that depending on the objectives of the study, their refinement and specification in the course of analytical work, the optics of the system approach can be changed, relatively speaking, by scaling the individual elements of the system as objects of study.