The present invention provides a novel and practical method for treating a perchlorate ion-containing liquid. The perchlorate ion-containing liquid is brought into contact with a weak base anion exchange resin, so that perchlorate ions are adsorbed to the weak base anion exchange resin, and then an acid is brought into contact with the resin, so as to remove the perchlorate ions from the weak base anion exchange resin to which the perchlorate ions are adsorbed. This makes it possible to repeatedly use the weak base anion exchange resin.