The analysis of theoretical development of a problem showed that the megalopolis is studied in line with social geography, economy, urbanistics, sociology. At the same time in social pedagogics and in social psychology the megalopolis did not become independent object of studying that constrains development of these industries of socio-humanistic knowledge. Relevance of the stated research for social and pedagogical and social and psychological knowledge will be defined by weak study of a problem of socialization of younger generations in the conditions of the megalopolis that constrains development of the theory of education and creates a number of difficulties in social practice. Purpose of the article. To give characteristic of the megalopolis as welfare and pedagogical social phenomenon. Research Methods. The methodology of a research was made the concept of socialization of the person (A.V. Mudrik) and a research of the megalopolis as mesofactor of socialization of the person. Theoretical methods: analysis a) researches on urbanistics and sociology of the city; b) demographic, ethnoconfessional and sociocultural structure of the population; c) statistical information on the sociocultural sphere; d) criminal statistics; e) conditions of sociocultural infrastructure; e) press and Internet resources. Empirical methods: a) the contemplate included observation; b) focus groups; c) expert estimates of experts, researchers and officials of the social sphere; d) profound studying of several municipal districts. Results. In a research characteristic of the megalopolis in a social and pedagogical foreshortening for the first time is given. The synthesized definition of the concept “megalopolis” and also set of methods of its studying is offered. The megalopolis is characterized as a difficult, polysynthetic, multidimensional phenomenon. Separately the architectural and planning environment of the megalopolis and its role in socialization of inhabitants is briefly described. It is differentiated the population as set of age, gender, sociocultural and social and economic strata and also ethnooccupation and confessional layers and communities is described. In either case interrelations of these characteristics with social education are outlined. Special attention is paid to the problems of the human capital, culture and a counterculture concentrated in the megalopolis, some aspects of their interrelation with social education are outlined. Conclusions. In general the research demonstrates that the megalopolis has a number of the sociocultural characteristics having both general character, and inherent in districts of the city, various for the objective reasons, thanks to which becomes the psychology and pedagogical phenomenon significantly defining socialization and social education of the younger generations living in it.