Provided are rice grains where various water-soluble high molecular substances are retained without applying pressure to the rice grains. Grains of mutant rice (wx/ae rice), which is deficient in both amylopectin branching enzyme (BEIIb) and amylose synthetase I (GBSSI), are immersed in an aqueous solution of a water-soluble high molecular substance such as digestion resistant dextrin, arabinogalactan, or polyphenol under ordinary pressure at room temperature and are then dried at 60° C. or less, preferably about 50° C., thereby producing rice grains impregnated with and retaining the high molecular substance.
