This paper evaluates moisture content effects on CO2 capture of an ion-exchange resin (IER) functionalised with a primary amine group. IER capacities were determined by breakthrough with an inlet gas containing 10 vol% CO2, nitrogen and various moisture contents. Three types of behaviour were identified according to humidity level. In saturated air conditions, the stoichiometry could be justified by carbonates and bicarbonates fixation. In dry conditions, we suspect a joint physical adsorption and reaction mechanism. For intermediate humidity, the stoichiometry of 1 CO2 for 1 amine group is consistent with a bicarbonate fixation or carbamic acid formation.