When a soft magnetic layer for a double layer type perpendicular magnetic recording medium is formed by a plating method, there is the problem of the occurrence of an isolated pulse noise called spike noise so that signal reproduction characteristics are lost. In order to solve this problem, provided are a surface-treated substrate for a magnetic recording medium comprising a substrate having a diameter of not more than 90 mm, and a soft magnetic plating layer comprising an alloy of at least two metals selected from the group consisting of Co, Ni and Fe, which is provided above the substrate, wherein the soft magnetic layer has a coercivity of less than 20 oersted (Oe) in a direction that is parallel to a substrate surface, and wherein a ratio of saturation magnetization to residual magnetization in a direction that is parallel to a surface of the substrate is from 4:1 to 4:3; and a magnetic recording medium comprising the magnetic recording medium substrate.