This invention relates to a sterilization agent for livestock bedding or a composting accelerator for organic waste or livestock bedding, comprising at least one Bacillus coagulans thermophilic bacterium or a combination of the at least one Bacillus coagulans thermophilic bacterium and at least one Bacillus subtilis mesophilic bacterium, as an active ingredient, wherein the Bacillus coagulans thermophilic bacterium as a preferable bacterium is viable at a temperature of 40 to 60° C. and the Bacillus subtilis mesophilic bacterium is viable at a temperature of 30 to 50° C., and the mesophilic bacterium also has a sterilizing effect on harmful bacteria in bedding; and to a method for sterilizing livestock bedding or a method for accelerating composting of organic waste or livestock bedding by using these agents each as an active ingredient.