After displaying information (10) on the surface of an outer wall (4) of a cell structure, a portion surrounding the displayed information (10) is coated with a coating agent to form a region permeated with a coating agent (24) wherein pores (22) of the outer wall (4) are filled with the coating agent in a section of the outer wall (4) on which the information (10) is displayed. The region permeated with a coating agent (24) prevents a catalyst solution from exuding from the inside of the outer wall (4) of the cell structure. According to a method for protecting the displayed information and the cell structure of which surface information is protected by the protection method, a displayed information portion after loading catalyst components is prevented from being colored, and the displayed information can be maintained in a readable state.