The present invention is to provide a mask blank enabling fabrication of a photomask having a structure where electrostatic breakdown is effectively prevented. To accomplish the object, the invention discloses a mask blank comprising a mask substrate, an electrostatic breakdown prevention film fully covering one side of the mask substrate, and a shading film formed on the electrostatic breakdown prevention film. The electrostatic breakdown prevention film is made of titanium, tantalum, titanium compound or tantalum compound. The transparent rate of the electrostatic breakdown prevention film is not less than 75%, for the wavelength of light in an exposure. The sheet resistance of the electrostatic discharge prevention film is not more than 100KΩ/□.