Optimum design of miniature hydrodynamic journal bearings at high speed of rotation is studied numerically. The critical speed due to oil-whip including the effects of viscous heating in the fluid film and elasticity of the journal is considered.The numerical parameters used in this paper are: the radius and the width of the bearings are 10mm， the span between bearings is 100mm and the viscosity of the lubricant is 27.2mPa・s at 313K (ISO VG32). The load and the speed of rotation are varied from 1 to 10⁴N and from 10 to 500s¹, respectively. The effects of the speed of rotation and the loads on the optimum radius of the bearings based on the maximum critical speed are presented. Moreover，the experiment was carried out and the pressure distribution，rise in temperature of the lubricant and leakage flow rate were measured. The theoretical results agreed with the experimental data.