Abstract: Liquid crystal additives(LCA ) have good antifriction property. But in previousreports,the contents which involved the research on the antifriction mechanism of LCA is very little. Here an experiment has been taken on a Falex tester under the given conditions of pressure,velocity and temperature to study the antifriction property of LCA. In the experiment,some nematic phase liqulti crystal,for example,4-hesoxy benzoic acid and n- 4-octyl benzoic acid have been selected as the additives to the HU-20 turbine oil,and the structure of liquid crystal dissolved in mineral oil and the morphology and element composition of wearing surface have been observed with the aid of X-ray diffraction,Auger electron spectroscopy and scanning electron microscopy. On the basis of what has already been achieved,the antifriction mechanism of LCA has been further analvzed.The results show that the LCA is dispersed in the oil in the form of fine crystal grains.During the rubbing procesess,the molecules of liquid crystal are adsorbed and arranged directionally on the surfaces of friction pair through their polar group-carboxy(-COOH),and form an antifrictional protectine layer. The formation of oxide film and the composition change of the ferrous oxide in surface laye rs significantly influence the antifriction effect of LCA. The LCA grains can fill in the micro concaviticS on the surfaces of friction pair,making them smcother and sliding easier.This is another important reason of the antifriction effect of LCA.