School regulations of 114 junior high schools were analyzed to investigate the nature of institutionalization in school. A coding system was developed which could classify a) regulations into task-relevant and task-irrelevant ones, b) situations and social relations prescribed in them, c) the degree of formalization and strictness, d) types of instructions (coercion, promotion, permission, dissuasion, and inhibition). The results indicated that a) schools had a median of 79.0 regulations of which those related to tasks numbered 19.8, and those not related numbering 55.0, b) in task-irrelevant rules, schools tried to control students' behavior in situations outside the school, and in social relations not directly concerned with school activities such as relations with peer group, family, and others, c) 48.5 rules were highly formalized an behaviors were prescribed in detail, d) many rules were coercive (45.0 regulations) and inhibitive ones (17.5) followed in number, while promotive (9.1), permissive (2.2), dissuasive (2.0) ones were relatively few. Categories which could indicate formalization were identified. The implication of the results for the institutionalization of educational organizations was discussed.