This study focuses on investigating the influence of microwave power (MWP) change on the morphology and size of Co3O4 nanoparticles (NPs), which was obtained from the thermal decomposition of cobalt oxalate precursor. The oxalate precursor was prepared via the microwave-assisted route in the presence of cetyltrimethylammonium bromide (CTAB) employing an MWP of 280 and 700W. Physicochemical properties of the prepared solids were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetry-differential thermal analyses (TGA-DTA). The results obtained indicated that the applied MWP has a crucial effect in controlling the morphology and the size of CoC2O4 center dot 2H(2)O as well as Co3O4 NPs. Acicular- and rod-like morphologies of both phases were obtained employing an MWP of 280 and 700W during the preparation, respectively. Further, both the prepared Co3O4 nanoneedles and nanorods are composed of net-like structure of interconnected nanocapsules. Moreover, although all the routes led to the same phase, additional difference existed in terms of surface Co2+ and hydroxyl-carbonate concentrations. Lower MWP favors high Co2+ and low cobalt hydroxyl-carbonate surface concentrations. (C) 2015 Elsevier B.V. All rights reserved.