In this study, poly(dimethyl diallyl ammonium chloride)/polyacrylamide (PDMDAAC/PAM), a hydrogel containing quaternary ammonium groups, was prepared and used as the adsorbent to remove the nitrate anion from aqueous solution. The effects of operating conditions, such as PDMDAAC content, contact time, pH, initial nitrate concentration, temperature, ion strength, and the presence of the competitive ion phosphate on the adsorption capacities were examined. The Langmuir, Freundlich, and Redlich-Peterson isotherms were used to describe the adsorption experimental data. The results indicate that the adsorption equilibrium can be achieved within 60 min, and the hydrogel has an increasing adsorption capacity with increasing PDMDAAC content up to 50 % (by weight). As-prepared hydrogel shows an appreciable adsorption capacity within the pH range of 5 to 9, and the calculated maximum adsorption capacity is found to be (1.1 to 1.4) mmol . g(-1). The hydrogel with higher PDMDAAC content is sensitive to the changes in the ion strength and competitive anion concentration. Effective desorption of nitrate is achieved using strong acid or base as the desorbing agent. It is proposed that two mechanisms are responsible for the higher adsorption capacity: one is swelling, and the other is electrostatic attraction.