In this investigation, incorporation of silica into natural rubber (NR)-reclaim rubber (RR) blend system was carried out by sol-gel technique at various sol-gel reaction temperatures. The effect of RR on silica reinforcement, hitherto unexplored, was studied for different NR/RR blend systems. The degree of reinforcement of sol-gel vulcanizates by equilibrium swelling method indicates that the reinforcing efficiency of the in situ generated silica by sol-gel technique increases with increasing reclaim rubber content. The reinforcing efficiency, tensile properties and thermal stability of sol gel vulcanizates (SGV) prepared at 50 degrees C become maxima as compared to SGV prepared at 30 degrees C and 70 degrees C. The amount of silica incorporated by sol-gel technique was determined by thermogravimetry analysis. It indicates that the thermal stability increases with silica content. Attenuated total reflection study indicates that RR forms bond with silica particles due to the presence of active functional site on RR. Scanning electron microscopy studies further indicate the coherency and homogeneity in the silica filled NR/RR vulcanizates. The microwave diagnosis of different SGVs was also carried out and the frequency dependence of dielectric permittivity (E') and loss (E) were measured. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers