[Problem] To provide: a bactericidal agent composition which can exhibit an excellent bactericidal effect in the presence of an organic substance and against biofilms； a method for producing the bactericidal agent composition； and a sterilization method using the bactericidal agent composition. [Solution] A bactericidal agent composition which comprises water containing ultrafine bubbles having a most frequent particle diameter of 500 nm or less and a bactericidal component. Preferably, the density of most frequent particles of the ultrafine bubbles are 10,000 particles or more and the density of ultrafine bubbles each having a particle diameter of 1000 nm or less is 1,000,000 particles or more. Fig 1.
