Abstract: A method and an apparatus for sharpening the surface of a grindstone for a pulp grinder. In the method a high-pressure water jet is obliquely projected on the surface of the grindstone for detaching bonding material between abrasive grains, without excessively wearing a medium between grinding segments.The apparatus comprises a nozzle, arranged to spray water obliquely onto the surface of the grindstone and a high-pressure pump for feeding high-pressure water through the nozzle. The nozzle is arranged to be moved by transfer means in the axial direction of the grindstone while the grindstone is being rotated.