A series of Nafion((R))/[organically modified silicate (ORMOSIL)] hybrid materials have been created by in situ sol-gel copolymerizations of tetraethylorthosilicate and semiorganic silicon alkoxide monomers. The trends in the mechanical tensile properties of these hybrid materials were largely rationalized in terms of the entrapment of the long sulfonic acid side chains in silicate or ORMOSIL structures. There is a significant increase in the mechanical strength relative to that of unfilled Nafion((R)) except in one case. Young's modulus is enhanced relative to that of unfilled acid form Nafion((R)) in a number of cases, although the degree of ductility is reduced relative to that of unfilled Nafion((R)). The filler fractions are beneath a critical value that would reflect percolation of a glassy, direct load-bearing silicate phase.