This article concerns the influence of different ZnO nanoparticle concentrations (0.001, 0.003, 0.005 and 0.01 wt%) along with operating parameters (i.e., pulsation intensity and flow rate of dispersed and continuous phases) and physical properties on mean drop size and drop size distribution in a horizontal pulsed perforated-plate extraction column for the toluene acetone water and butyl acetate acetone water systems (mass transfer direction from the dispersed phase to the continuous phase). According to the results, it is observed that the addition of nanoparticles has a remarkable influence on breakage and coalescence of drops and consequently their size distribution. Accordingly, adding nanoparticles reduces the interfacial tension due to internal turbulence caused by nanoparticles' Brownian motion inside each drop. It is found that drop size distribution will shift to the left and the density of small droplets will increase in the presence of ZnO nanoparticles in the column. Furthermore, new correlation is proposed to predict mean drop size in terms of operating parameters, physical properties and nanoparticle concentration. It is also found that the maximum entropy principle is suitable to predict drop size distribution in a horizontal extraction column. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.