More and more nanoparticles may be found in the aquatic environment. Effects of different nanoparticles (nano-Al2O3 and nano-TiO2) on the coagulation process in kaolin suspension (with or without humic acid) were investigated. The results indicated that when the pH was 7.0 in kaolin suspension, the strength factor with the presence of TiO2 increased from 28.79% to 48.69% and when the concentration of TiO2 was larger than 1.6 mg/L, the strength factor decreased to 23.39%. The removal efficiencies for Al2O3 were 58.27%, 62.73% and 47.3% under pH 6.0, 7.0 or 8.5. The removal efficiencies for TiO2 were 38.12%, 52.25% and 27.19%. When the concentration of DOC was 2.5 mg/L under pH 7.0, the recovery factor increased from 54.55% to 62.65% with increasing concentration of Al2O3 from 0.0 mg/L to 2.0 mg/L, and it increased from 54.55% to 67.74% for TiO2. PACl produced larger flocs, and this may be caused by higher charge neutralization ability and the electrostatic patch effect. The removal efficiency for TiO2 decreased from 52.25% to 22.13% with increasing concentration of DOC from 0 mg/L to 7.5 mg/L. The removal efficiency for Al2O3 decreased from 62.73% to 32.12%. (C) 2014 Elsevier B.V. All rights reserved.