A study has been made of the electrochemical etching of 99.99% aluminum foils at a current density of 50 mA cm(-2) in AlCl3-HCl solutions (1 M Cl-) at 80degreesC. The solutions were made by dissolving metallic aluminum into 1 M HCl solution, to give a Cl- concentration of 1 M. The number density of etch tunnels and the homogeneity of tunnel length decreased, and the mean pit size and its standard deviation increased with increasing Al3+ concentration. The results were discussed based on potential transients at a current density of 50 mA cm(-2), current-potential curves at a scan rate of 10 mV s(-1) and electrochemical impedance spectra.