To provide a method for inhibiting scales, effective for a bleaching tower, a washing tower and their peripheral pipings, installations, or the like, used in a bleaching process containing sodium hypochlorite on the production of craft pulp.

In this method for inhibiting scales in a process for bleaching craft pulp with sodium hypochlorite on the production of the craft pulp, the characteristic comprises adding 2-phosphonobutane-1,2,4-tricarboxylic acid in the bleaching process. The 2-phosphonobutane-1,2,4-tricarboxylic acid is preferably added in an amount of 0.1-100 ppm, more preferably 0.5-20 ppm. The amount of <0.1 ppm does not give a sufficient scale-inhibiting effect, and the amount of >100 ppm gives a sufficient effect, but does not give the improvement of the effect corresponding to the amount. Thereby, the amount of >100 ppm is not preferable from an economical viewpoint.