The stable oil-in-water Pickering emulsions were prepared using oxygen plasma treated carbon nanotubes (CNTs) as stabilizers. Some hydrophilic groups such as hydroxyl and carboxyl groups were introduced on the surface of the CNTs by plasma treatment. The plasma treated CNTs showed the improvement in dispersion stability in water as well as cyclohexane for a long time. The Raman spectra showed that the original properties of CNTs were retained after the plasma treatment differently from other chemical modification methods. The plasma treated CNTs had a favorable interfacial interaction with water to form the stable O/W Pickering emulsions. The formation of stable O/W Pickering emulsion was dependent on the CNT concentration, the plasma treatment period, and the sonication time.