Nanocrystalline iron manganite powder was synthesized using the sol-gel combustion process, with glycine as fuel. It was further calcined at 900 C for 8 h, resulting in the formation of a loose cubic FeMnO 3 powder with a small specific surface area, net-like structure and plate-like particles as confirmed by XRD, N 2 physisorption, FESEM and TEM analyses. The metal ion release was studied by ICP-OES and showed that less than 10 ppb of Fe or Mn ions were released by leaching in water, but 0.36 ppm Fe and 3.69 ppm Mn was found in LB (Luria-Bertani) bacterial medium. The generation of reactive oxygen species (ROS) was monitored in distilled water and bacterial medium and showed that FeMnO 3 particles do not generate O 2 c À ions with or without UV irradiation, but synthesize H 2 O 2 and show an antioxidative effect. Besides the higher stability of FeMnO 3 particles in aqueous solution they showed an inhibitory effect on Bacillus subtilis growth in LB medium even at low concentrations (0.01 mg ml À1), but not in BHI medium even at 1 mg ml À1. This study points out that the mechanism of antibacterial action of engineered metal oxides needs continued investigation and specific experimental controls.