This study was conducted to set the proper sterilization standards of casing soil for the stable production of buttonmushroom(Agaricus bisporus) from mushroom disease that occurs in infection of casing soil material. Changes of aerobic bacteriaare increased as the longer grow-out period and sharply increased after second flushes. Fluorescence Psuedomonas showed highdensity at high sterilization temperature and 100^oC treatment has extremely high density at 30 min and 60 min in casing 22 days.Density of thermophilic actinomyces is sharply increase from casing with soil and the highest density at 22 days of casing andrapidly decrease after first flushes. Sterilizing temperature of casing soil affects quality and quantity of button mushroom.Treatment of 60 min, 90 min at 80^oC and 30 min at 100^oC produced the highest mushroom yields, especially mushrooms yieldsof A grads were the highest at treatment of 90 min at 80^oC. Treatment of 60min at 100oC products many yields, however, thistreatment has low economic feasibility for its yields. Sterilizing temperature of casing soil has an effect on generating diseases andinsect pests. Treatment of 60 min, 90 min at 80^oC and 30 min 100^oC showed lower incidence than the other treatment. Althoughtreatment of 30 min at 100^oC causes low diseases and mushroom fly damage, it has low mushroom yields. Furthermore, althoughtreatment of 60 min at 100^oC has high mushroom yields, it causes high diseases and mushroom fly damage. Therefore the bestconditions for the sterilization of casing soils was 60 min and 90 min at 80^oC.