Fe-Mn bimetal oxide nanocomposite was synthesized by a new aeration co-precipitation method. For this purpose, the Fe3+ and Mn3+ in a molar ratio of 2:1 were simultaneously precipitated in the presence of excess oxygen. The physicochemical, structural and optical properties of the synthesized nanocomposite were investigated by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray analysis (EDX), X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Brunauer-Emmet-Teller (BET), and UV-Visible analysis. The FESEM images showed that the synthesized nanocomposite had a dominant spheroid-like shape and homogeneous morphological structure with many aggregated nanocomposite and rough surfaces. The average size of synthesized nanocomposite was 13.75 nm with a range of 10.33-17.48 nm. The EDX analysis confirmed the presence of Fe (25.23 wt%) and Mn (21.55 wt%) in the nanocomposite. The XRF analysis showed that the Fe-Mn nanocomposite contained 49.83% Fe2O3 and 29.36% Mn2O3. The XRD analysis confirmed that the nano composite had two peaks at 32.9 degrees and 36.5 degrees, which were respectively related to Mn2O3 and Fe2O3. UV-Vis absorption peaks of Fe-Mn nanocomposite was between 358 and 369 nm and the band gap energy was 2.06 eV. The BET specific surface area and pore volume of the nonocomposite were 244.79 m(2)/g and 0.6633 cm(3)/g, respectively. So, considering the spherical, uniform, and mesoporous structure with large surface area and pure volume, the aeration-co-precipitation, as an appropriate synthesis method, is suitable to synthesize Fe-Mn bimetal nanocomposite that can be widely used as a catalyst in photocatalytic oxidation or can be applied as a nano-adsorbent to remove pollutants from the contaminated water.