TiNi shape memory alloy samples annealed at 673K for 1h were irradiated within R-phase by 1.7-MeV electrons with different doses. The two-step martensitic transformation temperatures were measured by differential scanning calorimeter. The results indicated that the temperature M of the onset of R-phase-to-martensite transformation decreased with increasing electron dose. The electron irradiation had s a slight effect on the other transformation temperatures. The second lifetime of positrons determined by positron annihilation technology were lowered with increment of the irradiated dose. Relaxation of the elastic stress fields around the Ti Ni precipitates was the cause of 3 4 the observed change of the transformation characteristics because of the migration and accumulation of irradiation-induced point defects.