The material flow in friction stir welded 2014 Al alloy has been investigated using a marker insert technique (MIT). Results of the flow visualisation show that the material flow is asymmetrical during the friction stir welding (FSW) process and there are also significant differences in the flow patterns observed on advancing and retreating sides. Combining the data from all the markers, a three-dimensional (3D) flow visualisation similar to the 3D image reconstruction technique was obtained. The 3D plot gives the tendency chart of material flow in FSW process and from the plot it can be seen that there is a vertical and circular motion around the longitudinal axis of the weld. The influence of the pin geometry on material flow in FSW was studied. When the column and taper pin are used, there is a ‘hole’ defect in the vertical mixing plot. When the taper with screw thread pin is used, the vertical material flow is more obvious and there is no distinct ‘hole’. Viewing from the advancing side, the pin geometry will affect the position where minimal transport distance against the welding direction occurs.