(1) A tissue-covering medical material which comprises a soluble cellulose derivative having been made hardly soluble in water, which is used with a purpose of being embedded in the body or applied to the tissue, and (2) a method for producing the tissue-covering medical material as defined in (1), which comprises, as a method to make a soluble cellulose derivative hardly soluble in water, freezing and thawing an acidic solution of the soluble cellulose derivative, are provided.