In this work the effect of resistance welding parameters in thermoplastic composite materials was evaluated in terms of the resulting microstructure and fracture mechanisms of the welded joint. Processes parameters as power density and welding time were investigated. For the microstructural characterization, samples were prepared for polarized light optical microscope observations. DCB testing was performed for the determination of the fracture energy, GI, and short beam flexure as well. The results were correlated to the microstructural characteristics of the welded region, and with the fracture surface of the tested specimens. Welded specimens were also compared to solid laminates and the particularities of each fracture mechanism were discussed.