Recent development of OIM (Orientation Imaging Microscope) makes the measurement of crystal orientation easy and advanced computer technology allows us to conduct a detailed stress analysis of component with microstructure. In this study, a high-cycle fatigue test was carried out for a copper polycrystal, where the shape and orientation of each grain is measured by the OIM. Thirteen PSBs are found along the grain boundaries, and the location and slip system are different from those expected by the Schmid factor. FEM analysis is conducted for the copper polycrystal with the same orientation and shape. It reveals that the increase of resolved shear stress, tau(rss), of specific slip system due to the constraint of deformation between grains causes the unique slip behavior near the grain boundary.