Five different nanofluids have been prepared by use of two-step procedure, in which SiO2 nanoparticles with different volume fractions and hydrophobicities have been dispersed in butyl acetate as base fluid by applying ultrasonication method. Three different methods have been used to evaluate the nanofluids' stability: conventional sedimentation method, particle size analyser and UV-Vis spectrophotometric. As a quite novel research, these nanofluids were applied to a Rotary Disc Contactor with 91?mm diameter and 12 rotating discs to investigate breakage probability and the first critical rotor speed. The effects of nanoparticles' volume fraction and hydrophobicity, as well as rotor speed, mother drop size and continuous phase height on the breakage phenomenon have been studied. (C) 2011 Canadian Society for Chemical Engineering