Rice seed was treated by high proton beam irradiation up to 1,200 Gy in order to elucidate physicochemical properties of irradiated rice starch. The decrease of amylose content in two rice cultivars ranged 3.5 to 3.6% compared to the non-irradiated rice under the highest proton beam irradiation (1,200 Gy). Gel consistency in japonica rice cultivar Ilpum was significantly increased with increasing proton beam irradiation. Its values approached 9.7 in the Ilpum rice cultivar and 8.7 cm in the Hanmaum rice cultivar. The peak viscosity, hot peak viscosity, cool peak viscosity, and setback were significantly decreased with increasing proton beam dose. High proton beam irradiation caused a significant decrease in the onset temperature ($T_o$), peak temperature ($T_p$), conclusion temperature ($T_c$), and enthalpy change (${Delta}H$). Gelatinization range (R) in two rice cultivars was more broaden in higher proton beam irradiation than in low proton beam irradiation. The crystallinity degree of two rice starches irradiated with high proton beam was significantly increased and it ranged from 3.25 and 4.39% compared to the non-irradiated rice starches. It might be deduced that proton beam irradiation causes changes of starch, especially at high irradiation of proton beam.