MgO nanoparticles were synthesized by template-free reflux condensation approach. XRD and FTIR confirmed the formation of single phase MgO exhibiting cubic crystal structure. SEM and TEM analysis revealed the formation of MgO nanoflakes. The optical band gap of MgO nanoparticles estimated from UV DRS was in the range 5.40-5.45 eV. PL spectra of MgO nanoparticles showed visible emissions due to the formation of defects in the band gap region of MgO. Synthesized MgO nanoparticles exhibited appreciable photocatalytic activity for the degradation of methyl orange and methylene blue dyes under UV light irradiation. Results demonstrated that the origin of photocatalytic activity in MgO arises due to the existence of high concentration of native defects on the surface of MgO. (C) 2013 Elsevier B.V. All rights reserved.