The design of the fatigue life of a rolling bearing is based on the Lundberg-Palmgren theory. This theory suggests that the fatigue life of a rolling bearing is influenced by the size of the volume under shear stress. Thus, a rolling bearing with small balls is expected to display a different fatigue life from one with larger balls, even if their maximum contact pressures are the same. The reason for this difference is that the volumes that are under the shear stress between different-sized bearings are different. However, when the contact equivalent radius of a rolling bearing is 1 mm or less, there is no confirmation whether its fatigue life can be designed according to the Lundberg-Palmgren theory. For this re出on,the fatigue life of ball bearings with small balls is measured under a fluid lubricating condition. The results obtained are as follows. 1) The difference in ball size is not a significant influence on the fatigue life of the ball bearing. 2) The rolling fatigue life of a rolling bearing with small balls, as well as rolling bearings with typical sized balls, can be designed using the conventional method.