Abstract: In order to predict the ductile fracture of welded connections in steel structures due to earthquakes, the investigations were carried out on the calibrations and validations of micromechanics-based fracture models. The void growth model (VGM) and the stress modified critical strain (SMCS) model relate the micromechanism of ductile fracture (void nucleation, growth and coalescence) to macroscopic stress and strain fields. The VGM and SMCS model parameters for Q345 structural steel, the corresponding weld and heat-affected zone were calibrated by using the available tensile tests of notched round bars and the complementary finite element analyses (FEA). Seven local welded assemblies of beam-to-column connections were tested at monotonic tensile loading, and the fracture critical elongations were measured. The J-integral based fracture mechanics approach and micromechanics-based model VGM and SMCS were adopted to predict the fracture critical elongation of each specimen using the refined finite element model (FEM). The comparisons between FEA predictions and experimental measurements in fracture critical elongation indicate that the VGM and SMCS models could predict the ductile fracture of welded connections with reasonable accuracy, while the J-integral approach obtains quite conservative results. A general method that is only material dependant is proposed for the ductile fracture prediction of welded connections in steel structures.