Polyethyleneglycol (PEG) stabilized Ru nanoparticles (NPs) were synthesized by single pot rapid microwave (mu W) method in presence of glucose as reducing agent. The mu W reaction for different amounts of added glucose and PEG was monitored by UV-vis spectroscopy. Small sized NPs (2-5 nm) were obtained with appropriate amounts of glucose and PEG. The size of particles decreased with increasing mu W power and decreasing irradiation time (keeping input energy constant), as observed by dynamic light scattering and transmission electron microscopy, which means one has size control via preparation process. X-ray diffraction pattern confirmed hcp lattice of synthesized Ru-0 NPs. To demonstrate their usefulness, a model reaction was selected in which degradation of azo bonds of congo red dye was catalyzed by Ru NPs. This is first report where Ru NPs were employed in catalytic decolorization of an azo dye, which is an important application in waste water treatment. It was found that the NPs acted as an electron mediator in transfer of electron from reducing agent to azo bond. Rate of the reaction increased drastically by introducing Ru NPs in the system and decolorization of dye was accelerated by factor of 200, which is substantial improvement in facilitating this important reaction. (C) 2013 Elsevier Inc. All rights reserved.