Cationic hydrogels, poly(dimethyl diallyl ammonium chloride)/polyacrylamide (PDMDAAC/PAM), were prepared for the removal of congo red (CR) from aqueous solution. Process parameters affecting the adsorption efficiency were systematically investigated. The results showed that the calculated monolayer adsorption capacity of the cationic hydrogels was found to be 200 to 465 mg/g. The hydrogels showed appreciable adsorption capacities within pH range investigated. The adsorption process well obeyed pseudo-second-order kinetics and the Langmuir isotherm. The ion exchange dominated the whole adsorption mechanism. All the information suggests that the as-prepared cationic hydrogels show potential applications in the fields of wastewater treatment for the removal of anionic dyes such as CR.