A series of chlorided Pt/Al2O3 (both gamma and eta) catalysts were prepared and characterized for various physicochemical properties. The chloride content of the catalysts was found to increase with chloride treatment time up to a certain level and then decrease owing to prolonged exposure at high temperature. The surface area and pore volume of the catalysts were decreased by chloride treatment. The activity of the prepared catalysts were tested in n-butane isomerization. The platinum content of the catalysts was found to have no effect on catalytic activity up to 0.2 wt% whereas the chloride content of the catalyst strongly influenced the activity and a >20-fold increase in activity was observed on chloriding Pt/Al2O3 catalysts. The catalyst activity was found to be directly related to its acidity.