Abstract: Full ceramic bearings have been gradually applied to the motorized spindle of high speed CNC machine tools because of their excellent characteristics of self-lubricating, wear resistance, corrosion resistance, high stiffness and light weight. However, large radiation noise is produced in the process of the bearing operation. In order to explore the characteristics of radiation noise for the motorized spindle with full ceramic ball bearings, the sound pressure level of radiation noise in grinding and unmachined was tested. With the increase of rotational speed, the radiation noise increases gradually, and the radiation noise in grinding was larger than that in no-load operation. The radiation noise of grinding workpiece was more complex with the change of rotational speed. The magnitude of the radiation noise at different field points was different. The experimental results show that the sound field of motorized spindle with full ceramic ball bearing has directivity. The rotational speed is one of the main factors affecting the radiation noise of full ceramic ball bearing. The grinding load also has a great influence on the radiation noise.