Burr is formed at workpiece edge in most metal cutting methods. The burr formation mechanism in milling is, especially, complicated because of geometric variety of tools and workpiece shapes. Burr formation is considered to be plastic deformation of workpiece edge. One aspect of dominant factors is workpiece shape, which has effects on plastic deformation, and another aspect is deformation process in burr formation, which is classified into "sheared" and "hinged". These processes are controlled by exit order of cutting edges from the workpiece edge. In this study, burr size which formed with various geometry of tools and workpiece edge is measured. Moreover, the effect of in-plane exit angle on side burr size was analyzed with a finite element method (FEM). As the results, it was found that the in-plane exit and radial rake angle have great effect on both exit and side burrs in face milling because these formed the various deformation area at workpiece edge. Burrs formed on the hinged side possibly grow because the workpiece material, previous burrs or cutting chips remains on the burrs. To control the burr size and shape, it is important to control the deformation area at workpiece edge by in-plane exit angle and radial rake angle.