To provide a photomask cleaning method which brings about a high effect of removing residual sulfuric acid or foreign objects and can remove foreign objects effectively without fluctuating the transmission or other properties of the light-shielding layer (MoSiON film) in a phase shift photomask. A method of cleaning a photomask which comprises a first step of cleaning the surface of a photomask used as a master in the photolithography step in the process for the production of semiconductor device with a hot mixture of sulfuric acid and hydrogen peroxide to decompose organic objects present thereon and remove metallic impurities, a second step of removing residual sulfuric acid from the surface of said photomask, a third step of removing foreign objects attached to the surface of said photomask, and a fourth step of drying said photomask which has finished with said first, second and third steps, characterized in that said second step involves the removal of residual sulfuric acid from the surface of said photomask with anodic water and said third step involves the removal of foreign objects with cathodic water.