In this paper we propose it method for identifying of parameters of lubricated journal bearings which are named, in rotordynamics literature, Sommerfeld and Mass Number, respectively. The system analyzed belongs to the class of systems that are described by v, nonlinear second order differential equations for which we obtain the analytical response using Lie series. The method call be applied to a vast class of dynamical systems provided that they are described by smooth equations. This tool allows LIS to obtain the system response in recursive wily using PC-codes for symbolic Calculus. Also, the procedure involves only a few experimental data, making very quick the identification process. It is worth noting the application proposed does not take into account neither the issue connected to experimental data noise nor unavoidable noise that Occurs in measurement process. In system identification there is always concern about noise a robustness, issues that are over the goal of this paper.