Nanocalcium borates were hydrothermally synthesized using borax and calcium nitrate as row materials. The structure and morphologies of composites were investigated by FESEM, XRD and FTIR. The result shows that the thickness of the synthesized calcium borates is less than 100 nm. The tribological properties of the oleic acid modified calcium borates as lubricant additives in liquid paraffin were evaluated on fourball tester. The results reveals that the friction coefficient of the base oil with 0.5% calcium borates is decreased from 0.09 to 0.035, and the wear scare diameter is decreased from 0.68 mm to 0.35 mm under the test conditions of 392 N, 1 450 r/min and 30 min running.