To provide a new, extraction preparing process which produces effectively and economically the pectic substance useful in the food industry and medicine industry, from soybean seeds especially in the view point of the practical use of soybean resources.

The process for producing a high purity pectic substance from a leguminous plant, comprises (1) the step of heat treating the leguminous seeds and/or the residual material of the leguminous seeds together with water and thereby releasing a part between the seed coat section and the seed leaf section; (2) the step of breaking the seed coat section in a solvent in which the pectic substance is insoluble and thereby insolubilizing the pectic substance which exists in the part between the seed coat section and the seed leaf section; and (3) the step of isolating the pectic substance.