A method for fractionating a soybean protein into highly pure 7S globulin and 11S globulin efficiently in an industrial scale is provided, said method comprising warming a solution containing a soybean protein under a weakly acidic condition followed by fractionating at pH 5.6 to 6.6 into a soluble fraction and an insoluble fraction. If necessary, a treatment with a phytase may also be employed in the production method to fractionate into a 7S globulin and a 11S globulin.