Copper single crystal billets with a systematically controlled orientations were subjected to equal channel angular pressing (ECAP) for four passes in order to investigate the mechanism of gram fragmentation. It was found that the billet which exhibited shear bands after the first ECA-pass, was most fragmented m terms of grain size and orientation scattering after four passes via the so-called route Bc. The billets deformed via route C revealed a kind of pan-cake structure with less fragmentation The electron back-scattered diffraction (EBSD) evidenced that fiagmentation was appreciable at the intersection of shear bands which appeared in successive passes. It was shown that the crystallographic orientation in terms of the shear plane in a simple shear plays a key role in the formation of shear bands, and thus facilitating grain fragmentation, while the accumulative strain is of secondary significance.