Si atoms were successfully incorporated into the iron-oxide framework of ferrolite. The addition of silica to the reported synthesis system of ferrolite negatively affected the formation of ferrolite; however, by optimizing the water content in the starting materials, highly crystalline Si-incorporated ferrolite was obtained. Incorporation of Si was confirmed by changes in the average size of sod cages and chemical composition. Thermal analysis indicated the improved thermal stability of the Si-incorporated products. It was also found that a portion of guest Na+ can be replaced by NO3- and OH-.