Abstract: The structures and electrical and magnetic properties of Ni–Mn–Sn-based alloys are studied. Changing the crystal lattice type in the course of martensitic transformation is found to be accompanied by substantial changes in the electrical resistivity. It is shown that for all the alloys under study negative magnetoresistance is observed. The maximum magnetoresistance in a magnetic field of 18 kOe of ≈–45% was found for the Ni47Mn40Sn13 alloy. © 2023, Pleiades Publishing, Ltd.