The purpose of this investigation was to refine the grains of annealed 6063 aluminum alloy and to improve its yield stress and ultimate strength. This was accomplished via the equal channel angular extrusion (ECAE) process at a temperature of 200℃ using route A, with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels for as many as 6 passes. The experiments were conducted on an Avery universal testing machine. The results showed that the grain diameter decreased from 45 μm to 2.8 μm after 6 extrusion passes. The results also indicated that the major improvement in fatigue resistance occurred after the first pass. The subsequent passes improved the fatigue life but at a considerably lower rate. A maximum increase of 1100% in the case of low applied stresses and an approximately 2200% increase in fatigue resistance in the case of high applied stresses were observed after 5 passes. The improvement of fatigue resistance is presumed to be due to (1) a reduction in the size and the number of Si crystals with increasing number of ECAE passes, (2) the aggregation of Cu during the ECAE process, (3) the formation and growth of CuAl₂ grains, and (4) grain refinement of the Al-6063 alloy during the ECAE process.