Abstract: A three-point fracture test was taken out on single notched beams of ultra-high toughness cementitious composites (UHTCC),with three fiber volume fractions of 1.5%,2.0% and 2.5%,in order to investigate the fracture property of this material. Ductile fracture exhibits for this material. On the basis of nonlinear fracture mechanics,the double-Jcriterion,that is the starting point of ductile stage, J_IC,and the starting point of failure stage,J_IF,is applied to estimate the fracture toughness of UHTCC. When J< J_IC,there is no macrocrack; J> J_IF,the failure crack is localized; and J_IC< J≤ J_IF,the deformation develops stably. Based on the experimental results,the J_Rcurve of UHTCC has three stages,with the dividing points of initial cracking and crack localizing. Furthermore,equal fracture energy is required for the equal quantity of crack growth.