Gas-phase adsorption equilibria of,diluted mixtures of methyl-ethyl-ketone and isopropylanol on activated carbon were investigated. Experimental isotherms were determined by a constant volume method. Single-component adsorption isotherms were fitted by the frequently used Toth model with good accuracy. Then adsorption isotherms were determined for different binary mixtures (with different initial ratio of the two components). Binary mixtures adsorption isotherms were calculated using the adsorbed solution theory. Ideal adsorbed solution theory (IAST) could not represent experimental data, but it was observed that increasing amount of MEK led to higher nonideality of the mixture. Then UNIversal QUAsi Chemical (UNIQUAC) and nonrandom two-liquids (NRTL) models were considered to describe activity coefficients of the adsorbed phase. The fitted parameters of UNIQUAC model depend on the ratio of the two components, whereas the NRTL model is able to fit all experiments with the same parameters, whatever the initial ratio may be. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 3109-3119, 2010