An immunogenic composition containing leucocidin M/F antigen and capable of imparting a toxin-neutralizing activity to a ruminant animal as a subject animal. The immunogenic composition enables prevention of onset or reduction in symptoms of diseases caused by Staphylococcus aureus in ruminant animals. The leucocidin M/F antigen is a protein or peptide having at least a part of the amino acid sequence constituting the leucocidin M protein or a protein or peptide having at least a part of the amino acid sequence constituting the leucocidin F protein. The immunogenic composition may further contain a somatic antigen of Staphylococcus aureus.
