Friction stir welding is known for his capability to achieve a linear weld. However, more investigation on a curved friction stir weld trajectory is still required to industrialize this promising process. In the same perspective, this study is aimed at analyzing the influence of nonlinear tool trajectory in friction stir welding. The study considers a variety of circular trajectories on the plane plate and uses them for experimentation while considering different welding parameters of rotation speed feed speed, axial force and tilt angle. In FSW, the tool is generally needed to be tilted with a constant angle in the travel direction during welding process. Therefore, for circular trajectory, an adequate roll and pitch angle are assigned to the spindle in all tool positions. The paper presents the effect of circular trajectory on longitudinal and transversal forces generated during circular welding. The results are then compared with the experimental results which are obtained using linear FSW. Furthermore, the experimental investigation includes relationship between tool trajectory and weld quality.