This study fabricated nano-CeO2/biodiesel carbon soot (BCS) composites using the raw material BCS,which is the byproduct of biodiesel combustion and cerium salt and used as a novel lubricant additiveto PAO6 for steel/steel contact. Oleylamine modified nano-CeO2/BCS composites comprise abundant lipophilicgroups, and thus nano-CeO2/BCS composites exhibit good dispersion in PAO6. The tribologicalresults showed that nano-CeO2/BCS composites significantly improved the lubricating performances ofPAO6. In case of 0.1 wt% nano-CeO2/BCS composites dispersed in PAO6, the friction coefficient and wearvolume were reduced by 17.3 and 35.2%, respectively. The improved tribological properties were attributedto the composites rolling and forming of a lubricating film on the friction surface and the presence ofBCS and CeO2 in composites exerting a synergistic lubricating effect, which simultaneously improved thetribological properties of PAO6. This discovery contributes to the conversion of BCS into valuables andpromotes the high value utilization of BCS as a lubricating additive.