Geosynthetic clay liners (GCLs) are widely used as hydraulic barriers in cover and liner systems of waste containment facilities. They consist of a thin layer of sodium bentonite sandwiched between two geotextiles. Bentonites used in GCLs typically have a high swelling capacity and a low hydraulic conductivity. However, the severe exposure conditions encountered by GCLs in many geoenvironmental applications can deteriorate its hydraulic performance. This problem is addressed by treating the bentonite present in GCL using polymers. The current study evaluates the use of super absorbent polymer (SAP) for modifying the bentonite by adopting the in-situ polymerization technique. Design of experiments was used to determine the optimum proportion of chemical mix that gives the polymer the maximum water absorption capacity (WAC). An empirical model was developed using the MINITAB software. The influence of factors such as crosslinker, initiator and NaOH on WAC of the polymer was studied using surface and contours plots. At optimum, the synthesized polymer was found to absorb the water at about 300 times its own dry weight. Further, polymerized bentonite was developed with 30% polymer dose and its swelling capacity was evaluated using the free swell index test (ASTM D 5890). The results showed the improved performance of polymerized bentonite compared to untreated bentonite.