Abstarct: Optimization journal bearings are very important because of their numerous applications in various industries such as power plants, turbomachinery, electrical machinery, shipbuilding, and etc. thise thesis foucuses on the use of particle swarm algorithms in developing an efficient optimum design method for finite bearings and tilting-pad bearings. The approach optimizes baxsed on minimum film thickness, power loss and maximum film temperature. Results are presented for oil with various inlet temperatures. also for finite journal bearings have been optimized for a different pad angle. In this thesis, a numerical three-dimensionalthermo-hydrodynamic code has been developed to simulate the steady condition of tilting-pad journal bearing without restrictions on their size, especially length of bearings. In this program, Reynolds equations for oil flow in the gap between the shaft and the bearing pads are solved by using a numerical finite difference method with a successive over-relaxation scheme in this simulation. for closing the solution to the real conditions, oil viscosity changes with temperature is also taken into account.