An ultra-precision ball rotating displacement measurement setup based on laser focus deviation was presented. The setup is capable of measuring ultra-precision ball rotating displacement at nanometer sensitivity. The experiment results indicated that the method has high repeatability and potentially with high throughput. A dual-probe setup is also studied to evaluate diameter variation in a ball with errors introduced by misalignment, while spindle radial vibration being automatically eliminated. Optical probe-based ultra-precision ball displacement and diameter variation measurement are suitable for in situ application with high throughput and repeatability.