Keggin type Q(3)PW(12)O(40) nanoparticles (Q = cetyltrimethylammonium cation) were synthesized in water-in-oil (w/o) microemulsion consisted of water/cetyltrimethylammonium bromide/n-butanol/isooctane. Reaction of Na2WO4, Na2HPO4 and hydrochloric acid within water containing nanoreactors of reverse micelles resulted in the preparation of Q(3)PW(12)O(40) nanoparticles. The resultant nanoparticles were analyzed by physicochemical methods such as FT-IR spectroscopy, X-ray diffraction, energy-dispersive Xray analysis, thermogravimetric analyses (TGA-DTA), scanning and transmission electron microscopy and atomic force microscopy which show nearly uniform spherical nanoparticles with size of about 15 nm. Finally, catalytic activity of the Q(3)PW(12)O(40) nanoparticles was examined in the epoxidation of olefins with H2O2. The prepared nanoparticles acted as recoverable and reusable catalyst in the epoxidation of olefins with H2O2. (C) 2015 Elsevier Ltd. All rights reserved.