The role of acid activation of the montmorillonite matrix before pillaring and the effect of calcination temperature on the efficiency of Al-pillared acid-activated clay modified electrodes have been investigated. The electrochemical behaviour of untreated and pillared montmorillonites was compared with that of two pillared acid-activated montmorillonites. The pillared acid-activated montmorillonite modified electrodes present better electroactivity than the modified electrodes of the conventional pillared montmorillonite towards cationic and anionic redox active species. Mild acid activation of the montmorillonite matrix and a calcination temperature up to 500 degreesC lead to modifying materials that efficiently concentrate the cationic species. Lower calcination temperatures reverse the electrode activity. For anionic redox active species the best electroactivity was observed for pillared acid-activated montmorillonite films corresponding to a medium acid activation. In that case, a dependence of the electrochemical response on the pH was confirmed. The mechanism responsible for the observed cationic electroactivity was investigated and the behaviour of the Al-pillared acid-activated montmorillonite modified electrodes was attributed to the particular structure as well as the enhanced meso-external surface area and acidity of the clay films.