PURPOSE: To separate only a water-soluble component containing saponin as a film permeated solution simply and inexpensively, by substituting a methanol extracted solution of soybean with an aqueous system, making a water- insoluble component comprising almost all the extract into colloid.

CONSTITUTION: A methanol extracted solution of soybean is substantially substituted with an aqueous system, a water-insoluble component is made into colloid, treated by ultrafiltration, and a water-soluble component containing saponin is separated as a film permeated solution. In the substitution with the aqueous system, for example, the methanol extracted solution is not concentrated or concentrated, and water is added to the extracted solution. The treatment by ultrafilter is carried out preferably at normal temperature at 4kg/cm2 and the filter has a molecular weight of fractionation of about 6,000W10,000.