Background: In this study, the effect of processing parameters on the mechanical properties of friction-stir-welded polyamide (nylon 66) sheets is investigated. Methods: Commercial polyamide sheets with the dimension of 250 × 150 × 8 mm are used in experimentations. The processing parameters considered in the welding include: rotational speeds in five levels and traverse speeds in three levels. Tensile and impact tests are performed in order to evaluate mechanical behavior of welded sheets. Full-factorial design of experiments and also analysis of variance was performed in present study. Results: Results show that when rotational speed increases, weld strength first increases and then decreases. In other words, there is an optimum rotational speed in which the welded samples could obtain the highest tensile Strength. Regarding the traverse speed, weld strength decreases with increasing of the traverse speed. Conclusions: Obtained results show a significant relationship between considered properties and processing parameters through an analysis of variance (ANOVA) study.