tThis study focuses on investigating the influence of microwave power (MWP) change on the morphologyand size of Co3O4nanoparticles (NPs), which was obtained from the thermal decomposition of cobaltoxalate precursor. The oxalate precursor was prepared via the microwave-assisted route in the presenceof cetyltrimethylammonium bromide (CTAB) employing an MWP of 280 and 700 W. Physicochemi-cal properties of the prepared solids were characterized by means of X-ray diffraction (XRD), Fouriertransform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electronmicroscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetry-differential ther-mal analyses (TGA-DTA). The results obtained indicated that the applied MWP has a crucial effect incontrolling the morphology and the size of CoC2O4·2H2O as well as Co3O4NPs. Acicular- and rod-likemorphologies of both phases were obtained employing an MWP of 280 and 700 W during the prepara-tion, respectively. Further, both the prepared Co3O4nanoneedles and nanorods are composed of net-likestructure of interconnected nanocapsules. Moreover, although all the routes led to the same phase, addi-tional difference existed in terms of surface Co2+and hydroxyl-carbonate concentrations. Lower MWPfavors high Co2+and low cobalt hydroxyl-carbonate surface concentrations.