In the presence of ions with various hydrolysis characteristics, the water-molecule structure and surface charge on iron sludge colloids can be changed and the dewaterability of iron sludge will also be affected. Such effects were studied in the laboratory through determinations of zeta potentials and specific the resistance of Fe2O3 sludge particles. It was found from experiments in the presence of ions with various hydrolysis characteristics in the iron sludge solutions, that the dewaterabilities of iron sludges showed the orders Cl > Br > I and IO3 > BrO3 > C1O3 for anions, and Li+ > Na+ > K+ > Rb+ > Cs+ and Mg2+ > Ca2+ > Sr2+ ∼ Ba2+ for cations. In the presence of ions of different concentrations, the change in zeta potentials and the improvement of dewaterabilities of iron sludge particles followed the order lO−2M > 10−3M > lOM for both IO3− and Li+; although the change in zeta potentials increased with the ion concentration for I and Cs+, the dewaterabilities of iron sludges were depressed with increasing ion concentrations.