Natural fibers whose surfaces have been plated with titanium oxide. Scoured wool is immersed in a solution of acetic anhydride (10 wt.%) in DMF (90 wt.%). The solution containing the wool is heated to 50 °C and kept at this temperature for 30 minutes to make the wool anionic. This wool is washed with water and then immersed in a 2.0 % owf aqueous solution of at least either of a titanium alkoxide and titanium fluoride at ordinary temperature for 30 miunutes. Subsequently, a 0.5/1/1 (by weight) mixture of boric acid, citric acid, and D,L-malic acid is added to the aqueous solution in an amount of 0.5 % owf. The wool is thus treated at 50 °C for 30 min and then washed with water. Thus, natural fibers whose surfaces have been plated with titanium oxide can be obtained.