Fatigue response was investigated for a low activation ferritic steel, F82H, under in-beam (dynamic), post-irradiation (static) and unirradiation conditions with 17 MeV protons at 60°C. Miniaturized specimens with a side notch in gauge were tested in a stress-control mode with triangular wave at two different loading ratios; R (σ_max/σ_min) = 0.44 (375 MPa ↔ 165 MPa) and R = 0.2 (375 MPa ↔ 75 MPa). Fracture surfaces were examined by a scanning electron microscope (SEM) for all specimens. Some evidence of the dynamic irradiation effect on fatigue response was observed in both fatigue tests and the SEM evaluations. The dynamic effect was more influential than the static effect at R = 0.44, while it was suppressed at R = 0.2 where the larger loading amplitude was imposed on the specimen. Balance between defect flux and fatigue damage development would control the dynamic irradiation effect.