The performance of a spray liquid-liquid extraction column at two mass-transfer directions was experimentally studied in the presence of silica nanoparticles. Toluene-based nanofluid drops containing 0.0005-0.01 vol % silica nanoparticles were dispersed in aqueous phase and acetic acid (AA) transfer between phases was investigated. The experiments were performed at fixed volumetric flow rates of dispersed and continuous phases. Maximum enhancement of 47.4% and 107.5% in overall mass-transfer coefficient, respectively, for mass-transfer direction of dispersed to continuous phase and vice versa were achieved for drops with 0.001 vol % silica nanoparticles. These enhancements can be referred to Brownian motion of nanoparticles and induced microconvection. The results showed that nanoparticles are more effective in augmenting AA transfer from continuous to dispersed phase. Probable reason is that smaller diameter and lower internal turbulence of drops in this transfer direction increase dispersed phase resistance potential to be manipulated by Brownian motion of nanoparticles. (c) 2015 American Institute of Chemical Engineers AIChE J, 62: 852-860, 2016