The influence of microstructure on the electrochemical properties of an Al-5 wt% Cu binary alloy which was severely deformed by equal-channel angular pressing (ECAP) has been investigated in a borate-boric acid buffer solution containing Cl- ions at pH 8.3 and 25 degrees C by potentiodynamic polarization test. The anodic polarization results showed that pitting potentials of ECAPed Al-Cu alloy samples were higher than that of the sample without ECAP and increased with repetitive ECAP passes. The pitting corrosion attack of Al-Cu alloy samples took place in the surroundings of Al2CU (theta) phase. It is considered that the grain refinement of theta phase and the solid solution generated in Al matrix during ECAP process are responsible for the improvement of the corrosion resistance of ECAPed Al-Cu alloy.