There are some researchers who work in the design of the electronic circuits. In this paper, the mathematical models of four different and nonlinear electronic circuits are presented. The electronic models are nonlinear, because the model of the diode is nonlinear. In addition the comparison between the real circuits and the simulation of the mathematical models of the circuits are presented. The future research is to work in the design of the presented electronic circuits. The article presented some promising patents on the modeling of four nonlinear electronic circuits. Keywords: Mathematical model, electronic circuits, state space system