[en] Ti-50.6 at.% Ni shape memory alloy specimens were irradiated under the austenite state (parent phase) using a tandem accelerator by 18 MeV protons with doses of 1.53 x 10¹³ and 1.53 x 10¹⁴ H⁺/cm². The microstructure and phase transformation of the specimens before and after irradiation were examined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). After the irradiation the parent phase (austenite) was stabilized. R-phase transformation start temperature and the reverse martensitic transformation finish temperature decreased with the increasing proton fluence. They decreased about 13 K and 6 K at a dose of 1.53 x 10¹⁴ H⁺/cm², respectively. The reverse martensitic transformation start temperature and R-phase transformation finish temperature were not affected by the proton irradiation. There is no observable change in the microstructure after irradiation for the low atom displacement probability. The variation of the transformation temperature was assigned to the local stress fields and change in the ordering degree of lattice generated by proton irradiation