Experiments and finite element simulations have been carried out to assess the warm pre-stressing effects on the effective fracture toughness of the high-chromium reduced activation tempered martensitic steel Eurofer97. The experiments have been conducted on sub-sized compact tension specimens in the low ductile to brittle transition region. The specimens have been pre-loaded at room temperature before being tested at low temperature. A clear increase of fracture toughness measured after warm pre-stressing has been found that is discussed in the light of the finite element calculations. In particular, a discussion of the role of the residual compressive stress field, triaxiality level and accumulated equivalent plastic strain respectively on the fracture toughness increase after warm pre-stressing is analyzed. It is shown that a change of the local criterion for fast-fracture has to be considered, which results from the pre-deformation. (C) 2013 Elsevier B.V. All rights reserved.