PROBLEM TO BE SOLVED: To provide an environmentally friendly bactericidal composition which shows a high bactericidal effect even in a short time on sporulation bacteria such as Bacillus cereus and Paenibacillus bacteria which are peracetic acid resistant bacteria.SOLUTION: Provided is a mixed composition comprising an acidified chlorite and a peroxide such as hydrogen peroxide and peracetic acid, having a highly effective bactericidal action on Bacillus cereus and Paenibacillus bacteria which are sporulation bacteria having high chemical resistance. The composition liquid allows sterilization in a practical action time in the areas of sterilization and cleansing of production apparatuses for food products and soft drinks, containers and packaging materials, and the like.