Abstract: Surface-modified cenosphere was prepared and used as a lubricating additive in calcium complex grease. Friction and wear of steel against steel lubricated by calcium complex grease with and without surface-modified cenosphere were evaluated on a MMW-1P face-to-face tribo-tester. The lubricating mechanism of the surface-modified cenosphere was discussed. The morphology of the surface-modified cenosphere was observed on an optical microscopy (OM). The results showed that the surface-modified cenosphere can be well dispersed in base oil (500SN). The friction and wear of steel tribo-pair under lubrication of grease can be improved using surface-modified cenosphere as an additive. Specifically, at a rotating speed of 1200 r/min and a applied load of 200N, the friction coefficient and the wear were reduced by 37.5% and 33% for 500SN oil doped with 1% cenoshpere particles.