Abstract: The chromatogenic reaction conditions of silicomolybdic blue in spectrophotometric determination of silicon dioxide in ilmenite samples were studied. Sample was decomposed with NaOH-Na2O2 flux and the melt was digested with acid solution. Na2SO3 was then added into the solution and the sample solution was heated in water bath to eliminate the interferences from H2O2 and Ti. The method has been applied to the determination of silicon dioxide in National Standard Reference Materials. The results are in agreement with the certified values with the precision of 0.34％～2.24％RSD (n=7).