PURPOSE: To effectively prevent decarburization in heating the high Mn non- magnetic slab by coating the antioxidant on the surface of the slab of a specific composition consisting of C, Si, Mn and Fe, covering the steel sheet thereon, and executing the hot rolling at a specific temperature.

CONSTITUTION: The antioxidant is coated on the surface of the slab having the composition consisting of, by weight. 0.15-0.70% C, 0.10-3.00% Si, and one or more kinds of 12-30% Mn, and, as necessary, 0.05-3.00% Ni, 0.05-8.00% Cr, 0.05-3.00% Mo, and the balance Fe with inevitable impurities, and satisfying the inequality 60C+Mn≥36%, and a part of or the whole of the surface is covered by the steel shell. This stab is heated to the temperature to meet the inequality 'heating temperature' ≤[20(60C+Mn)/3+900°C] and the inequality 'heating temperature' ≤1250°C to execute the hot rolling. This constitution suppresses the decarburization of the surface layer part in heating the slab of the high Mn non-magnetic steel. The slab obtained in this method indicates the surface magnetic permeability of ≤1.02 only by removing the surface scale, and the surface grinding is not necessary.