Abstract: The carbon nanotubes(CNTs)/oleic acid (OA) composite was prepared by filling OA into CNTs, then the nanofluid was prepared by the CNTs/oleic acid composite as additive. The conductivity and wettability of the nanofluid were investigated, and the effects of the content, acidification time, test temperature and electric field on the above properties were also studied. The results show that the composite is successfully formed with a filling rate of about 20%. During the preparing process, the end face of the CNTs is chemically modified, and the best acidification time is about 8 h. Compared with the acidified CNTs, the CNTs/OA composite has better surface activity and dispersion in the base solution, which can better improve the conductivity and wettability of the nanofluid, and the optimal content of the composite is about 0.1%. Under the condition of electrowetting, the wettability of the nanofluid with the higher content of the composite can be improved more obviously with the increase of voltage. This may be because the conductivity and capacitance of the CNTs are improved after the filling of OA, and the nanofluid prepared by the composite also has better conductivity and capacitance.