Ultra-fine aqueous dispersions of zinc oxide were prepared by a combination of wet ball-milling and ultrasonication in the presence of various concentrations of a process control agent (PCA). The particles in the dispersions were characterized by dynamic light scattering (DLS) and zeta potential measurements. Six hours of ball-milling of the zinc oxide dispersion containing 3 wt.% PCA followed by ultrasonication resulted in the formation of particles having size below 500 nm. (C) 2014 Elsevier B.V. All rights reserved.