The aim of the study was to investigate the effect of vibration welding parameters on the structure of welding region in polyamide 66 joints. The quality of joints was examined under an optical microscope using polarized light. Differential scanning calorimetry (DSC) was used to study the influence of welding parameters: vibration amplitude (a), welding pressure (pz) and weld time (tz) on the melting temperature and the crystalline phase content in the weld as well as the base material of the joints. For low welding pressure and amplitude values, an amorphous phase was dominant in the welding region (Fig. 6a), while for higher values of these parameters an increase in the crystalline phase content was observed (Fig. 7). The mechanical strength of PA 66 joints was evaluated using a static tensile test (Table 3). Maximum tensile strength was in the range of 70 to 77 % of the value for the base material.