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To improve the lipophilicity of ZnO nanopowder in lubricating oil and analyze the surface modification mechanism, stearic acid, oleic acid, and HTAB-SL were selected as surface modifiers. ZnO nanopowders were prepared and modified in a single step by dielectric barrier discharge plasma assisted ball milling for 10 h. The ZnO nanopowder was characterized and analyzed by SEM, FTIR, TG-DSC, x-ray diffractometer, x-ray photoelectron spectroscopy, lipophilicity determination, COF test, etc. The results showed that the size of ZnO nanopowder was 40–100 nm. The results also revealed that the lipophilic groups –CH2 and –CH3 of modifier were successfully modified by ZnO nanopowder. Meanwhile, hydroxyl groups –OH of ZnO nanopowder chemically adsorbed with hydrophilic carboxyl groups –COO– of modifier. The lipophilicity of modified ZnO nanopowder was significantly increased. The COF of oil sample with modified ZnO nanopowder was smaller than that of oil sample with unmodified ZnO nanopowder. The modification mechanism was attributed to the coupling action of plasma, modifier, and mechanical forces of ball milling. The research demonstrated that modified ZnO nanopowder is more suitable as lubricating additive. [ABSTRACT FROM AUTHOR]