Abstarct: During the past few decades gas-lubricated bearings have received great attention from practical and analytical tribologists. The rapid growth of gas bearing technology is mainly due to its wide range of engineering applications such as precision machine tools, high speed aircrafts, nuclear reactors, textile spindles, dental drills, etc. Gas-lubricated journal bearings have the advantage of negligible friction, cleanliness and easy availability of air as the lubricant. However, poor dynamic stability due to low viscosity is a major problem. Therefore, the investigation of dynamic behavior is necessary to avoid settling of the system in a region where its control is severe. In this dissertation the dynamic analysis of a rigid rotor supported by noncircular gas-lubricated journal bearings is studied. Three types of noncircular gas bearins such as two, three and four-lobe bearings have been considered. To obtain pressure variable a finite element method is employed to solve the nonlinear Reynolds equation in dynamic state. Initial conditions for dynamical state are selected from the equilibrium position of the rotor center in the static state and the related pressure variable. The motion equations of the rotor and the Reynolds equation are solved together using the Runge-Kutta method to estimate position, velocity and acceleration at each time step. The solutions are regarded as initial conditions for the next time step. To analyze the behavior of the rotor center in the horizontal and vertical directions under different operating conditions, the dynamic trajectory, the power spectra, the Poincare maps and the bifurcation diagrams are used. Parameters such as rotor mass, bearing number and preload have been considered to investigate nonlinear dynamic behavior of system at two aspect ratios of 1 and 1.5. Results of this study show how the complex dynamic behavior of these types of system comprise the return to equilibrium position of the rotor center in the static state, -periodic and quasi-periodic of the rotor center and contact between the rotor and bearing with changes in the system parameters. Therefore, undesirable behavior can be avoioded for the rotor center by choosing suitable values for these parameters. Results indicate that the three types of noncircular bearings will rank from the stability standpoint with four-lobe having the highest stability, and two-lobe the lowest.