The dependence of irradiation temperature, neutron dose, and Cr content on irradiation hardening and embrittlement has been investigated for oxide dispersion strengthened (ODS) ferritic steels irradiated from 290 to 600°C up to the maximum neutron dose of 0.75 dpa. Irradiation hardening and embrittlement of the materials strongly depend on the irradiation temperature. While neutron dose increases from 0.01 to 0.21 dpa, the ODS steels with Al show a saturation of irradiation hardening but the no-Al ODS steel has an increase in the hardening. The higher the Cr content, the more significant the irradiation hardening and embrittlement of ODS steels irradiated below 420°C. Interestingly, the ODS ferritic steels exposed to neutrons show little change of tensile elongation, compared to 9Cr JLF-1. Furthermore the ductile-brittle transition temperature (DBTT) shift of ODS steels increases with the increasing irradiation hardening, indicating that the increase of yield strength due to radiation induced hardening increases the DBTT and thus a reduction of hardening is effective to reduce the DBTT shift.