We calculated the energy consumed for phase boundary motion in a Ni 52 Mn 23 Ga 25 single-crystalline sample during martensitic transformation using a boundary friction phenomenological theory. It was found that the energy consumed for phase boundary motion is 13.14 J/mol, only a small part of the latent heat of martensitic transformation. Furthermore, the results of transformation loops measured by ac magnetic susceptibility proved that the thermal hysteresis of martensitic transformation is in direct proportion to the volume fraction of martensite. It was also indicated that the thermal hysteresis of martensitic transformation originates from the friction of phase boundary motion.