[en] This paper reports on a Mg-substituted material with nominal composition Bi₂Sr₂Ca₃Mg₂Cu₆O_x, prepared by partial substitution of Ca by isovalent Mg in the 2256 composition of Bi-Sr-Ca-Cu-O, studied by the measurements of electrical resistance, magnetic susceptibility and x-ray diffraction pattern. Results show the existence of a superconducting phase with onset T_c at 112l.5 ± 1 K along with a minor phase with onset T_c = 88 K. The material retained superconducting characteristics (Meissner effect and T_c^onset) even after a period of six months