Abstract: A four-ball friction tester was used to investigate the tribological properties of lithium base grease using ultrafine silicon material (Si-Al type) as additive. The steel ball wear surface was characterized by optical microscope, scanning electron microscope (SEM) and energy dispersive spectrometer. The results show that anti-wearing ability is improved significantly but no effect on the antifriction performance. Compared with base grease, when the Si-Al additive is 0.5%, the wear scar diameters are reduced 22.37%,48.97% at loading of 392 N and 588 N, respectively, indicating the best anti-wear effect. After surface modification, the Si-Al additive powder is easier to dissolve in oil, but the tribological performance of the modified powder did not significantly change. Results of SEM and EDX show that in the process of long wear, a lubricating film mainly composed of SiO2,Fe2O3,Al2O3 is formed on the wear surface which has more notable tribological properties.