In this study, catalyst particles (the main component is Al2O3-SiO2) were removed from the fluid catalytic cracking slurry oil by adding a polyacrylamide flocculants (1200 mu g/g) and a ammonium citrate aqueous solution weighting agent (10% by weight of the slurry oil) at 95 degrees C, and then settled for 18 h. The ash content which determined by the muffle stove was considered as a criteria for measuring the efficiency of sedimentation. The size and distribution of the catalyst particles, before and after sedimentation, were analyzed using a laser particle size analyzer and a light transmission microscope. The results showed that the removal efficiency could reach 95.12% when both the flocculants and weighting agent were added. However, either the flocculants or weighting agent applied individually could only obtain inferior removal efficiencies of 87.04% or 68.76%, respectively. It would be attributed to the synergistic effect between the two agents. Moreover, it was also found that the flocs were rapidly formed from original catalyst particles and the flocculants firstly. Then the weighting agent provided assistance for the sedimentation of the flocs, of which the process was identified as the control step. The sedimentation process established in the experiment might play a role in the industrial removal of catalyst particles from slurry oil in the future. (C) 2018 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.