Recently, biosynthesis of nanoparticles has attracted scientists' attention because of the necessity to develop new clean, cost-effective and efficient synthesis techniques. In particular, metal oxide nanoparticles are receiving considerable attention in a large variety of applications. However, up to now, the reports on the green synthesis and characterization of nanocrystalline Ruthenium oxide (RuO2) are relatively few compared to some other metal oxides. In this paper, we report for the use of plant extract (Acalypha indica) in the biosynthesis of ruthenium oxide nanoparticles of dimensions 6-25 nm. The synthesized nanomaterials were characterized by Fourier transform infrared (FT-IR) spectrum analysis to confirm Ru-O symmetric stretching. X-ray diffraction (XRD) confirms the formation and the crystalline nature of ruthenium oxide nanomaterial. Further, these nanoparticles were found to exhibit high antibacterial activity against four different strains of the bacteria like Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens and Staphylococcus aureus. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.