Abstract: Present study proposed new identification method for the nonlinear dynamic system. Firstly, suppose that the original system is expressed by Hammerstein model then the transfer function of the model can be changed into a linear form, thus generating a middle model. The parameters of the middle model are obtained by a Bacterial Chemotaxis Optimization (BCO) algorithm. Finally, through the relationships of the parameters of middle model and those of Hammerstein model, the parameters of Hammerstein model are derived. Thus, the original system is identified. The feasibility and efficiency of the presented algorithm are demonstrated using numerical simulations.