Silicon monoxide (SiO) has a high-expected capacity and long cycle performance, but the first cycle's charge–discharge efficiency was lower than that of a conventional anode material. Recently, we have reported that the irreversible capacity was able to be suppressed based on the crystallinity of SiO. In order to decrease the oxygen defect and improve the crystallinity of SiO, Fe2O3 was reacted with SiO as an oxygen source then heat-treated at 800 °C. When the sample of the mixed SiO and Fe2O3 at a molar ratio of 1:0.2 was heated, Fe2SiO4 (fayalite) with the Pbnm olivine structure was uniformly formed on the SiO surface. It was confirmed that the efficiency of the first cycle's charge–discharge capacity improved in comparison to the conventional SiO.