Abstract: The effect of temperature on the fracture toughness of weld thermal simulated X80 pipeline steel in ductile-to-brittle transition (DBT) regime is studied. A large number of fracture toughness (as denoted by crack tip opening displacement, CTOD) tests together with finite element analyses are carried out using single edge notched tension specimens at various temperatures (-90℃, -60℃, -30℃ and 0℃). 3D finite element models of the tested specimens are used for the numerical simulation. It is concluded that fracture toughness CTOD values decrease with decreasing temperature. The tendency of brittle fracture with decreasing temperature is significant. The transferability of the true stress-strain curves obtained from weld thermal simulated round tensile bar to the fracture mechanics specimen works very well. The temperature shows only a slight effect on the material hardening behavior. As compared with the experimental results, the 3D model can precisely predict CTOD values at different temperatures considered in this study.