The characteristics of filler gel developed in the silica filled rubber systems were described in relation to the carbon gel. Two kinds of filler gel were considered. The one is that the filler gel corresponds to a rubber component entrapped within a secondary structure formed by silica particles (agglomerates), which is similar to occluded rubber in carbon gel. By a utilization of bi-functional coupling agent, chemical bonds are formed between rubber molecules and silanol groups on silica particles, which is the other type of filler gel. The fraction of filler gel in the filled rubber is dependent on the agglomerate size and the sort of coupling agent. By the utilization of silica with less number of silanol groups on the particles and by the introduction of coupling agent, the size of agglomerate decreased leading to the decrease in the fraction of filler gel in the systems. The tensile properties of silica filled rubber vulcanizates were also discussed in relation to the filler gel.