The method of structural identification nonlinear dynamic systems is offered in the conditions of uncertainty.The method of construction the set containing the data about a nonlinear part of system is developed.The concept of identifiability system for a solution of a problem structural identification is introduced.The special class of structures S for a solution of problem identification is introduced.We will show that the system is identified, if the structure S is closed.The method of estimation the class of nonlinear functions on the basis of the analysis sector sets for the offered structure S is described.We showed, as on S a preliminary conclusion about a form of nonlinear function to make.We offer algorithms of structural identification of single-valued and many-valued nonlinearities.Examples of structural identification of nonlinear systems are considered.