Boron carbide (B4C) has been mainly used in fast reactors as a control rod. The life-time of B4C control rods is limited by Pellet-Cladding Mechanical Interaction (PCMI) failure due to the swelling of B4C pellet. Helium, which is generated by the nuclear reaction of B10, causes the pellet swelling. Application of hafnium (Hf) hydride as a control rod is discussed in this paper, since the generation of He 4 is not an issue in the nuclear reaction process of Hf with neutrons. A control rod of Hf hydride is considered for use in fast reactors, sincefast neutrons generated in the driver fuel region are moderated and are efficiently captured in the Hf-hydride region of a control rod assembly. The nuclear reaction process of Hf with neutrons is expressed by Hf 1777(n,γ)Hf178(n,γ)Hf179. The Hf178, which is generated by a neutron capture reaction of Hf 177, has also a large neutron capture cross section. This implies that the Hf hydride control rod is superior to the B4C control rod in performance of long life use. The Hf-hydride control rod has been designed with the extended life of five to ten years in which the experimental data of the Zr-hydride were mostly referred due to the lack of data of Hf-hydride. The researches on Zr-hydride have been carried out much more than those on Hf-hydride since Zr-hydride is widely employed as a neutron moderator in nuclear reactors.