Six kinds of choline chloride (ChCl)/diols deep eutectic solvents (DESs) with different alkyl chain lengths and hydroxyl positions were prepared, which are easily synthesized and biodegradable. Tribological and bearing tests show that ChCl/ethylene glycol (EG) has the best performance on the surface of Si3N4/GCr15 tribo-pairs. Compared with PAO10, friction coefficient, wear scar diameter, bearing vibration, and friction torque decreased by 71 %, 28 %, 34.8 %, and 24.6 %, respectively. ChCl/EG, which has the shortest alkyl chain length and hydroxyl distance, has the highest molecular polarity. Such a dense and stable chemisorption film is formed and the lubrication performance is improved, which is confirmed by the inconspicuous tribochemical films. Consequently, ChCl/EG serves as a potentially superior lubricant for Si3N4 hybrid ceramic ball bearings.