To evaluate the effects of temperature varying neutron irradiation of the V-4Cr-4Ti alloys with small addition of Si, Al and Y, microstructure observation and micro Vickers hardness test were carried out after one cycle varying temperature neutron irradiation at the Japan Material Test Reactor (JMTR). On a temperature increase from 200 to 350°C, the hardness of the alloys decreased. It is possible to explain the appearance of a vacancy-rich state after the temperature change and subsequent mutual disappearance of interstitials and the vacancies. Following the temperature change from 375 to 500°C, the hardness of the alloys increased, therefore, the vacancy-rich state might not appear due to stable defect clusters formed at the lower temperature conditions.