The present invention provides oral compositions which contain interferon.alpha. (IFN.alpha.) asan active ingredient for preventing and/or treating periodontal disease. Thenumber ofcausative microorganisms of periodontal disease can be suppressed byadministering thecompositions into the oral cavity. IFN.alpha. of the present invention canproduce a sufficient effecteven when administered at a very low dose. Furthermore, the compositions ofthe presentinvention can also be readily administered to animals such as dogs byformulating them into feedor such.
