The research analyzes the social ontology of the American philosopher B. Epstein. Social ontology studies the nature of the social world: what are its main elements and how they come together. There are different theories in modern social ontology: the theory of structuration, the theory of communicative action, social constructivism, critical realism. B. Epstein opposes psychological theories of social ontology and ontological individualism in explaining the social world. B. Epstein distinguishes between ontological questions about the social world and causal relationships between events. The initial category of social ontology for American philosopher is a social fact. To establish a social fact, two actions are necessary: to give an ontological explanation of the existing social fact and to find facts that determine the conditions necessary for a social fact. Accordingly, B. Epstein distinguishes between two projects: the project of the foundation of a social fact and the project of fixing a social fact. The project of the foundation of a social fact provides an ontological explanation of a social fact, studies the conditions for the presence of social facts. The fixation project explores what gives rise to the conditions of the basis for social facts. The ground relation and the fixation relation are not causal relationships. A social fact must have diachronic constituent elements, which is, in particular, a test of social theory for truth. The article also discusses the theory of social facts by J. Serle. The theory of J. Serle B. Epstein refers to a psychological concept based on the collective acceptance of certain rules by the community. This position does not seem to be entirely correct, since J. Searle, in understanding the nature of a social fact, relies on social institutions, and the fact itself refers to institutional facts.