This paper discusses how urban institutions affect urban form. It presents an introduction of the position of urban institutions into the research framework of new institutional economics, discusses the relationship between institutional reform and development of urban morphology, and carries out a comparison on New York, Hong Kong, and Barcelona in four aspects, i.e., policy-dominated type(formal and informal), regulatory strategy(compulsory and incentive), policy benefi ciary(public and private), and the role of the government(manager and mediator), to attempt to ascertain in what specifi c ways institutions directly or indirectly affect changes in urban texture and urban form. Thereupon, it argues that the release of institutions may not achieve its predicted purpose. On the contrary, the form of a city, generated unexpectedly and spontaneously within the scope of rules will to some extent prompt the transformation of old institutions. Finally, it indicates that the interaction between “effect” and “feedback” is actually a circular causal reaction. It presents an introduction of the position of urban institutions into the research framework of new institutional economics, discusses the relationship between institutional reform and development of urban morphology, and carries out a comparison on New York, Hong Kong, and Barcelona in four aspects, ie, policy-dominated type (formal and informal), regulatory strategy (compulsory and incentive), policy benefi ciary (public and private), and the role of the government (manager and mediator) to attempt to ascertain in what specifi c ways institutions directly or indirectly affect changes in urban texture and urban form. Thereupon, it argues that the release of institutions may not achieve its predicted purpose. On the contrary, the form of a city, generated unexpectedly and spontaneously within the scope of rules will to some extent prompt the transformation of old institutions. Finally, it indicates that the interaction betw een “effect ” and “feedback ” is actually a circular causal reaction.