Abstract: A new numerical differentiation method with local optimum by data segmentation is proposed. The segmentation of data is based on the second derivatives computed by a Fourier development method. A filtering process is used to achieve acceptable segmentation. Numerical results are presented by using the data segmentation method, compared with the regularization method. For further investigation, the proposed algorithm is applied to the resistance capacitance (RC) networks identification problem, and improvements of the result are obtained by using this algorithm.