Orientation relationships between neighboring grains in a semi-continuously rheocast Al-5%Cu alloy billet by mechanical stirring were investigated by EBSP measurements. The state of microscopic segregation was also compared with that of a stir-free billet using TEM. Although some low angle grain boundaries existed except for the high angle ones, the special twin boundaries could scarcely be observed. At the stir-free billet, high copper concentration at eutectic phase once decreased rapidly as going into the matrix and the concentration still reduced slightly up to 1 or 2 at%. Similar concentration profiles were measured across the small grains in the stirred billet. In contrast to these, near constant concentration region with 1 at% were widely observed within the large grains.