The aim of this study was to develop topical hydrogels containing diclofenac potassium (DP) at 1% w/v concentration using conventional hydrophilic hydroxypropyl methyl cellulose (HPMC, 50cPs) and modified hydrophobic hydroxypropyl methyl cellulose (HPMC, 90L grade). The differences between in vitro release profiles of both types of polymer based hydrogels were studied using model dependent equations. Three formulations were prepared from hydrophobic HPMC at 1%, 1.5% and 2% (w/v) concentration. Other two formulations were prepared from hydrophilic HPMC at 12% and 15% (w/v) concentration. Hydrophobic formulations of higher viscosity with small quantity of polymer show higher release compared to hydrophilic formulations of lower viscosity with higher polymer concentration. Combined effect of swelling and erosion leads to anomalous diffusion in case of hydrophobic HPMC based hydrogels whereas only swelling leads to Fickian diffusion in case of hydrophilic HPMC based hydrogels. The formulations follow Higuchi release pattern as well as Weibull model.