The highly exfoliated Ti.sub.3C.sub.2T.sub.x nanosheets were synthesized by selective etching of the starting material of Ti.sub.3AlC.sub.2 using 40 % concentrated HF solution at 65 °C for 5 h. The effect of HF treatment temperature on the exfoliation degree was investigated by characterizing the morphology and microstructure of the Ti.sub.3C.sub.2T.sub.x nanosheets using SEM, XRD, and TEM. The results showed that the exfoliation degree of Ti.sub.3C.sub.2T.sub.x was increased with increasing temperature. The role of the termination groups produced during HF treatment on the exfoliation degree was discussed. The tribological property of the prepared Ti.sub.3C.sub.2T.sub.x nanosheets as additives in PAO8 base oil was measured. The maximum reduction of friction and wear was achieved under additive concentration of 0.8 wt% for the highly exfoliated Ti.sub.3C.sub.2T.sub.x nanosheets. The different effects of Ti.sub.3C.sub.2T.sub.x additives on the average friction coefficient and wear volume were analyzed, respectively.