PURPOSE: To obtain the titled complex easily absorbable in plant body, utilizable for the culture of edible plant and useful for the prevention and remedy of cancer, diabetes, cardiac disease, etc., by reacting a monosaccharide with germanium oxide in the presence of an alkali.

CONSTITUTION: The objective complex can be produced by reacting a monosaccharide (e.g. fructose) or a sugar alcohol (preferably mannitol or sorbitol) with germanium oxide in the presence of an alkali preferably in an aqueous medium under heating preferably at a molar ratio of 1:1.