The present invention provides an aqueous solution of a sterilant of peracetic acid series for use in aseptic filling comprised predominantly of hydrogen peroxide, peracetic acid and water wherein a pH of the aqueous solution is 2˜4, a ratio of the concentration of hydrogen peroxide/the concentration of peracetic acid is 0.7 or less, and the concentration of peracetic acid is 500˜3000 ppm as well as a sterilization method wherein the sterilant thereof is used. The sterilant of peracetic acid series exhibits an excellent sterilizing effect even at an extremely low concentration of peracetic acid and so is economically advantageous. What is more, washing of the sterilant with sterile water after sterilization of a container is attained by injecting sterile water even for a short period of time to such level that the sterilized container can be filled with foods and drinks, so that the sterilant is remarkable in economical value and working efficiency. The sterilization method is carried out by heating the sterilant of peracetic acid series and/or a container for foods and the like or the interior surface thereof at 60° C. or higher to obtain more effective sterilizing effect and can be used in a recycling system, so far as a ratio of the concentration of hydrogen peroxide/the concentration of peracetic acid be maintained.