A reference low-activation vanadium alloy NIFS-HEAT-2 was neutron-irradiated at 450 °C and below, in order to estimate the resistance to low temperature irradiation. DBTT of NIFS-HEAT-2 was -85 °C after irradiation up to 8.5 dpa at 450 °C in Na atmosphere, while DBTT was below -196 °C for 3.7 dpa at 430 °C in Li atmosphere. On the other hand, DBTT was lower than about -90 °C for the irradiation up to 0.1~1 dpa at 60, 290 and 400 °C. The DBTT shift was increased with increasing hardness after neutron irradiation for limited irradiation conditions. The mechanisms of DBTT shift and irradiation hardening at low temperature was discussed.