Magnetic Iron oxide film with the closeness of stoichiometric Fe₃O₄ (magnetite) has been prepared onto a non-conductive quartz glass substrate maintained at 293 K by light-assisted solution chemical reaction in an aqueous solution containing iron (III) nitrate hydrous and dimethylamineborane (DMAB). Fe₃O₄ film with smooth surface of 3.2nm in root-mean-square-roughness (Rms) was grown at 293 K and showed 480emu/cc in saturation magnetization and 150 Oe in coercive force. Raising the solution temperature gave the increase in Fe³⁺ constituent and decrease in saturation magnetization. The film prepared at 333 K was identified as a mixture of Fe³⁺, O^2-, and OH^- constituents and showed no magnetization. The resistivity ranging from 0.23 to 450Ωcm was obtained depending on solution temperature and was higher than that for the bulk material. This will be attributed to the non-stoichiometry of Fe²⁺/Fe³⁺ ions in Fe₃O₄ film.