Killer spectra were investigated to select killer yeast strains to inhibit the growth of wild yeasts that cause aerobic deterioration of silage. Kluyveromyces lactis IFO 1267 was characterized by its rapid killing activity and wide spectrum against the target yeasts. Crude killer protein produced by K. lactis IFO 1267 or inoculation of the cell itself inhibited the growth of the target strain, Saccharomyces cerevisiae IFO 0304 (in liquid or in solid culture), particularly when lactose was used as carbon source instead of glucose.