Excess water production cause serious technical and economic issues including corrosion, loss of productivity, scaling and etc. Various chemical and mechanical methods have been developed to isolate water source in the formation. Among chemical methods polymer-gel treatment is one of the proven solutions in which gel block is placed into high permeable water channel in order to isolate the water source. Most common polymer that is used for water shut-off treatments is Polyacrylamide (PAM) due to its availability and low cost. However in harsh reservoir conditions stability of gel based on PAM is unsatisfactory. Present study focuses on enhancement of bulk gel composition by addition of nano Silica. The effect of nano Silica on gel properties such as gel stability, strength, gelation time, bound/free water content, residual resistance factor was investigated. The results shows that nano Silica addition into bulk gel shortens the gelation time and strengthens the gel. Addition of nano silica significantly reduces syneresis of the gel and nano silica significantly improves the blocking ability of the gel by strengthening the bulk gel and increasing the adsorption. Furthermore, even after aging at 105 °C for 30 days the RRF for the gel with 1% nano silica is still sufficiently high. This observation is explained by syneresis decrement of bulk gel caused by nano Silica.