A theoretical framework to explore the urban social structure is required to answer the question “what is the basic structure of city”. Such a framework may comprise five perspectives : “area”, “social action”, “social group”, “social class and social stratum”, and “institutional complexes”.<BR>The urban structure as analysed from the perspective of “area”, called areal structure or community structure, has been so far the exclusive subject matter of the human ecologist, but it has to be studied not ecologically but sociologically.<BR>The perspective of “social action” has not been given due consideration, notwithstanding its basic methodological importance. Analysis from this perspective may be made in terms of three conceptually distinctive “systems of action” -economic, cultural and political.<BR>The perspective of “group” directs our attention to the analysis of the group structure in the city. Groups to be taken up in this respect are : industrial groups, family groups, labor groups, locality groups, political, groups, cultural groups, study or recreation groups, and aggregative groups. Group structure in the urban society may be made clearer by exploration into the interrelationships among these categories of groups than by the study of each category.<BR>Regarding the perspective of “social class and social stratum, ” the most important point is the conceptual distinction between “class” and “stratum”, and empirical analysis of the structure has greatly complicated these two concepts. The focus of such analysis may be on the middle class.<BR>The perspective of “institutional complexes” is to relate the social structure of the city to the total society. The former indeed constitutes a part of the latter, but it is a pivotal part. Thus it may be a dependent variable on one hand, but an independent variable on the other in this perspective.<BR>Studies in urban sociology that have been madethus far from each of these five perspectives indicate that the level of progress and the degree of elaboration varies with different perspectives, and that the difference of the basic viewpoint, derived from the difference of schools one follows, still remains unsettled. Hence, what we need now is the fundamental reexamination of urban studies, even if it may seem a mundane reexamination.