A process for producing an aqueous chlorous acid solution in which chlorous acid,which is safe for the human body, is easy to handle, and less generates chlorinedioxide, is yielded and used as a bactericide for a pretreatment in food processing. To an aqueous sodium chlorate solution is added sulfuric acid or an aqueous solutionthereof in such an amount and concentration that the pH of the aqueous solutioncan be kept at 2.3-3.4 to thereby react them and generate chloric acid. Subsequently,hydrogen peroxide is added to the chloric acid in an amount which is equal to orlarger than the amount necessary for a reduction reaction to thereby yield chlorousacid. Any one of inorganic acids, inorganic acid salts, organic acids, and organicacid salts, or two or more thereof, or a combination of these is added to the aqueoussolution containing chlorous acid yielded, whereby the chlorous acid can bepresent for long and the pH of the aqueous solution is regulated to 3.2-7.0. Thus,high bactericidal power is imparted thereto.
