Physical Chemistry Section, Jadavpur University, Calcutta-700032 Department of Chemistry, Visva Bharati, Santiniketan, Birbhum, West Bengal, India Manuscript received 6 December 1976, revised 28 March 1977, accepted 17 May 1971 Pure molecular adsorption of carboxylic acids (formic to n-butyric), mono- and dichloroacetic acids and hydrochloric acid has been studied with an anion-exchange resin, Amberlite-IRA-400, in its respective anion forms. The order of molecular adsorption of these acids on the respective anion forms of the resin is, hydrochloric <formic<acetic <propionic<n-butyric <monochloroacetic < dichloroacetic. For the carboxylic acids, molecular adsorption increases with the increase In chain length of the acids. The adsorption of the strong acid, HCL, is very small. Also it is known that not the carboxylate ions but the undissociated acids are molecularly adsorbed by the resin. But here it is found that the molecular adsorption of the chlorosubstituted acetic acids is considerably higher than the carboxylic acids studied, though the dissociation constants of the chlorosubstituted acetic acids are much greater than those of the carboxylic acids. Molecular adsorptions of the carboxylic acids by the nitrate, sulphate and chromate forms of the same resin have also been studied. The order of molecular adsorption of these acids by all the salt forms of the anion-exchange resin is the same as obtained for the resin containing the same counter-anions as the acids. The acids ate most strongly held by the chromate form of the resin and least strongly by the nitrate form.