We report on the swelling behaviour of thin maleic acid copolymer films in dependence of pH and ionic strength. The response of the polymer films was studied by quartz crystal microbalance with dissipation monitoring. It was found that solution's pH and ionic strength can be separately used to adjust the swelling of the maleic acid copolymer films. While the pH affects the degree of dissociation of the maleic acid groups, ionic strength triggers the interaction of the resulting charges along the polymer chains. The dominance of electrostatic interactions in the system was obvious from the maximal extension of the grafted polymer chains at very low ionic strength. Tuning the expansion of grafted polymer chains by pH and ionic strength can be utilized in various applications of biointerfacial research to adjust the physicochemical properties of polymer thin film coatings.