PURPOSE: To purify carrageenins useful in the fields of drugs, food, and toiletry industrially and advantageously by heat-treating carrageenins with hydrogen peroxide under hydration conditions in the presence of an inactive, water- miscible organic solvent.

CONSTITUTION: Carrageenins [example: beta (1→3)-D-galactose, etc.], are heat- treated in the temp. range of 60-120°C with 4% hydrogen peroxide water under hydration conditions in the presence of an inactive, water-miscible organic solvent such as methanol, ethanol, isopropanol, acetone, dimethylformamide, and actonitrile to be decolorized, a white suspension is filtered and washed with mixed liquid containing 95% ethanol and distilled water on a filter for distribution. Next, carrageenins on the market are purified by drying them in a vacuum oven after final washing with 95% ethanol being executed. The concentration of the hydrogen peroxide is desired to be 0.1-25% based on the weight of the carrageenins.