A method is proposed to identify nonlinear joint characteristics of a structure by means of measured data. The relation between the joint force function and the response of the system is established by use a position index matrix. The parameters of the joint force function are estimated by means of a least squares strategy. The parameter estimation can be done in time domain and also in frequency domain. Especially, when there is no excitation on the joint degrees of freedom only a part of the responses of the system are needed to identify the nonlinear joint parameters. The validity of the method is demonstrated by computer simulations.