We have studied the dechlorination/destruction of octachlorodibenzo-p-dioxin and octachlorodibenzofuran on alumina. The acidity of the alumina is an important parameter for the dechlorination of these compounds. Alkaline alumina is a better dechlorination agent than acidic alumina. Metal chlorides are less effective dechlorination catalysts than alumina. The dechlorination of octachlorodibenzo-p-dioxin and octachlorodibenzofuran on alumina proceeds probably via an electrophilic substitution mechanism.