In this study, nano-scale magnesium oxide particles were synthesized by means of flame spray pyrolysis and sol-gel techniques. Phase structures, morphologies, particle size, specific surface area and optical band gap were determined using an X-ray diffractometer (XRD), scanning electron microscope (SEM), particle size analyzer, Brunauer-Emmett-Teller (BET) specific surface area analyzer and UV diffused reflectance spectroscopy (UV DRS), respectively, In order to determine photocatalytic activity of the nano-scale particles, aqueous methylene blue (MB) solutions were employed. The photocatalytical degradation rates of MB solutions were determined through absorbance measurements performed via UV-vis spectrophotometer. Fourier transform infrared spectroscopy (FTIR) studies confirmed the formation -OH hydroxyl and other groups provide by MB solutions, after photocatalytic studies. It was found that both flame spray pyrolysis and sol-gel synthesized MgO nano-scale particles exhibited appreciable photocatalytic activity for the degradation of MB dye under UV light irradiation with small differences. Moreover, the effects of particle size and surface area on the photocatalytic properties were investigated in detail. (C) 2015 Elsevier Ltd. All rights reserved.