The morphological characteristic of a pit produced by the localized corrosion of sputtered Al-1wt.%Si-0.5wt.%Cu alloy thin film on silicon wafer in acidic chloride solution was investigated by using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The pitting potential was determined from the potentiodynamic polarization measurement. From the SEM observation, a pit obtained from the potentiostatic experiment in the acidic chloride solution showed a characteristic feature of circular bands around the pit bottom. The analysis by AES revealed the circular bands and the center of the pit were mainly composed of aluminium oxide and silicon oxide arising from the silicon wafer substrate, respectively. It was suggested that the pit in Al-1wt.%Si-0.5wt.%Cu alloy thin film quickly becomes two dimensional. The mechanisms of pit initiation and growth for the Al alloy thin film were discussed in terms of the two dimensional (2-D) nature of the pit.