In order to convert the used engine oil (UEO) to a fine chemicals, the properties of engine oil (EO) and UEO were initially compared by FTIR, H-1 NMR, and thermal behavior analyses. The UEO composition was first modified by sulfonation and then separated through separating funnel. Results showed that the as-prepared product, sulfonated UEO (SUEO), exhibits the properties of a surfactant. The surface tension of the aqueous SUEO solution was 34.64 mN m(-1) at the critical micellar concentration of 3.02 g L-1, which was one half of 72.27 mN m(-1) of distilled water. Up to 0.3 wt.% SUEO was used as a dispersant for coal-water slurry (CWS), and the viscosity of CWS was 170 mPa s when the content of coal powder was 65 wt.% at shear rate of 100 s(-1), and the rheological behavior belonged to pseudoplastic fluids. Experiments on the stability of CWS containing 0.3 wt.% SUEO demonstrated that the penetration ratio reached 37.8% after 15 days, which was higher by 12.1% than that of CWS without dispersant. Compared with commercial dispersants sodium lignosulfonate and sodium dodecyl sulfate, SUEO displayed a good performance for either liquidity or stability of CWS. In addition, the possible reason for the excellent behavior of CWS prepared with SUEO was discussed. Overall, this study provided a new disposal and updated way for UEO. (C) 2016 Elsevier Ltd. All rights reserved.