Abstract: An experimental investigation on double-K fracture parameters and fracture energy of ultra-high strength concrete is presented. In the tests, the compressive strength was up to 115.8 MPa and the dimensions of three-point bending specimen beams were 480 mm ? 120 mm ? 60 mm. Initial fracture toughness, unstable fracture toughness, and fracture energy were calculated from the data of initial cracking load, peak load, incipient crack opening displacement, etc. The results indicate that no obvious relationship exists between double-K fracture parameters and initial crack-depth ratios of the tested ultra-high strength concrete. At a fixed initial crack-depth ratio, double-K fracture parameters and fracture energy all increase with the increasing compressive strength.