The postirradiation fracture toughness of Type 347/348 stainless steel was investigated using 5.08-mm thick three-point bend specimens tested at 427°C. The J_Ic values were determined using the single-specimen unloading compliance technique in accordance with ASTM Test Method for J_Ic, A Measure of Fracture Toughness (E 813-81). Equivalent values of plane strain fracture toughness, K_Ic, were computed from experimentally determined values for several fluence levels ranging from 2.3 to 4.8 × 10²² neutrons (n)/cm² (E >1.0 MeV) and for irradiation creep of 0.0, 0.6, 1.1, and 1.85%. The test matrix involved four variables: fluence, creep, helium content, and heat-to-heat variation. Hence, separation of the individual effects of these variables on the K_Ic values was not possible due to limited irradiated material. However, the results show that an interpolated trend exists, that is, K_Ic decreases with increasing combinations of fluence, creep, and helium content. These results also suggest that irradiation creep has less effect on reducing K_Ic than has been suggested previously.