Provided is a method whereby a sterilized viscous base can be easily produced at a high sterilization efficiency. The method for producing a sterilized viscous base (base no. 5) comprises : a heat sterilization step for heat sterilizing an acidic solution of a viscosity-imparting agent (base no. 2) which shows a higher viscosity in a neutral range than in an acidic range; and a neutralization step for, after the heat sterilization step, neutralizing the heat sterilized product (base no. 3) of the acidic solution of the viscosity-imparting agent by adding a base thereto.