A simple sonochemical method was developed to synthesis uniform sphere-like Co3O4 and Mn3O4 nanocrystals. Epoxidation of styrene and cyclooctene by anhydrous tert-butyl hydroperoxide over the prepared Co3O4 and Mn3O4 nanocatalysts was investigated. The results of conversion activity were compared with bulk Co3O4 and Mn3O4. Under optimized reaction conditions, the nanocatalysts showed a superior catalytic performance as compared to the bulk catalysts. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface area, were used to characterize and investigate the nanocatalysts. (C) 2010 Elsevier B.V. All rights reserved.