To provide a lubricant for a hydrodynamic bearing having excellent long-term reliability by enabling a suitable base oil to be selected by judging the high-quality base oil satisfying the evaluation of heat resistance required for the hydrodynamic bearing based on initial data.

This lubricant for the hydrodynamic bearing is obtained by selecting and preparing the base oil and the lubricant having a little change of the viscosity at a low vaporized amount by the control of the initial purity of the base oil. As a result, the cost and a test period for selecting the base oil and the lubricant can be extremely reduced, and the selection can be precisely carried out.