A process for preparing high-purity bisphenol A by estimating on line slurry concentration of a bisphenol A-phenol adduct in a crystallizer on the basis of a material balance and a heat balance around the crystallizer and thereby maintaining said slurry concentration at a prescribed level to precipitate the crystals of said adduct. The slurry having a constant concentration can be always fed to a slurry separating step, thereby enabling steady operation of the slurry separating step. Thus, the process is useful for enhancing productivity. As a result, extraordinary adhesion of the impurity-containing filtrate to the crystals of the bisphenol A-phenol adduct can be inhibited in the slurry separating step, and hence high-purity bisphenol A can be obtained.