The present invention relates to a method for sterilizing microbial cells and to sterilized microbial cells, in which microbial cells or a culture containing microbial cells is treated with a polyethylene glycol-based nonionic surfactant so that almost all of the microbial cells are sterilized while the enzyme activity expressed in the microbial cells is maintained at a high level. In detail, the present invention relates to a method for sterilizing microbial cells and a material containing the sterilized microbial cells, in which the microbial cells are sterilized using a polyethylene glycol-based nonionic surfactant that can be used for foods so that the microbial cells are sterilized to be used in food production. Further, the present invention relates to a material containing sterilized microbial cells that can be used in processes for preparing tagatose, in which Corynebacterium genus microbial cells that produce Galactose and/or Arabinose isomerase are sterilized using a polyethylene glycol-based nonionic surfactant.