Abstract: In the present work, the irradiation hardening behavior of a Chinese low-activation ferritic/ martensitic steel CLF-1, a candidate for fusion reactor blankets, is studied. Specimens were irradiated with high-energy ¹⁴N and ⁵⁶Fe ions at the terminal of a cyclotron to three successively increasing damage levels of 0.05, 0.1 and 0.2 displacements per atom (dpa) at about −50 °C. The energy of the incident ions was dispersed to 11 successively decreasing grades using an energy degrader, thereby generating an atomic displacement damage plateau in the specimens from the surface to a depth of 25 μm, which is sufficiently broad for the Vickers hardness test. Eight different loads (i.e. 98 mN, 196 mN, 490 mN, 980 mN, 1.96 N, 4.9 N, 9.8 N and 19.6 N) were applied to the specimens to obtain the depth profiles of the Vickers hardness by using a microhardness tester. Hardening was observable at the lowest damage level, and increased with increasing irradiation dose. A power-law correlation of the Vickers hardness with the damage level (HV0=1.49+0.76 dpa^0.31) is proposed. Testing with a nano-indentation technique was also performed, and a linear relationship between the Vickers micro-hardness and the nanohardness (HV0=0.83H0) was observed. A comparison with other RAFM steels (CLAM, JLF-1, F82H, EUROFER97 etc.) under neutron or charged particle irradiation conditions shows that most of the RAFM steels exhibit similar power-law exponents in the dose dependence of irradiation hardening. The difference in the irradiation hardening may be attributed to differences in microstructure prior to irradiation.