The present invention provides oral compositions which contain interferon α (IFNα) as an active ingredient for preventing and/or treating periodontal disease. The number of causative microorganisms of periodontal disease can be suppressed by administering the compositions into the oral cavity. IFNα of the present invention can produce a sufficient effect even when administered at a very low dose. Furthermore, the compositions of the present invention can also be readily administered to animals such as dogs by formulating them into feed or such.
