[en] The magnetization of superconducting In-Mg alloys with a concentration of magnesium from 2 to 12.6 at % was measured. These measurements indicate that all the specimens were one-phase and type-2 superconductors. The dependence of Hsub(c2)(0) on Mg concentration has been estimated. A sharp increase of Hsub(c2)(0) and tsub(c) is observed for Mg concentrations between 2 and 4 at.%. Thisis caused by a change from a tetragonal into a cubic structure for alloy. (author)