In this paper, an on-line algorithm for identification of sandwich systems with backlash is proposed. In this method, the sandwich systems with backlash can be transformed into a special model where all the model parameters are separated based on the so-called key term separation principle. In this case, a piecewise model with linear coefficients combining with nonlinear variables is obtained. Thus, an extended recursive identification algorithm is used to estimate the parameters of the proposed model. Finally, the modeling results on an X-Y positioning stage are presented.