Recently, manganese oxides have been considered in the environmental remediation, MRI diagnosis and drug and pharmaceutical industries. Different numbers of physicochemical and biological methods have been reported for the preparation of nanoscale manganese oxides. Although manganese oxide biogenesis by bacterial species has been recognized as the major Mn-oxidizing agent in nature, in this research, for first time, we demonstrated the process which used to produce bixbyite-like Mn2O3 nanoparticles by isolated aerobic bacterium from Persian Gulf water. The 16SRNA sequencing showed that this isolate belong to a gram-negative Acinetobacter which produced nano Mn-oxide crystal particle. Characterization of complement morphology, size and chemical structure of these particles were determined by TEM, SEM, EDAX, XRD and FTIR. The data showed that this bacterium could produce nanosized extracellular bixbyite-like Mn2O3 which depend on enzymatic pathway.