Abstract: The present invention relates to a method for preparation of a powder with no unpleasant odor at a higher &bgr;-glucans content and a larger bulk density but with a smaller bacterial number, from the fruit body of Maitake or Yamabushitake, comprising immersing the fruit body of Maitake or Yamabushitake in a heated aqueous acid solution followed by drying and grinding. The aqueous acid solution includes aqueous solutions of inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid and edible organic acids such as acetic acid, citric acid, malic acid, tartaric acid and succinic acid. Acetic acid or citric acid is preferable in terms of cost and effect.