Uniaxial elongational viscosity of SiO2/(acrylic polymer/epoxy (AP/EP)) suspensions with various SiO2 volume fractions (I center dot) in a blend of acrylic polymer and epoxy was investigated at various temperatures (T). The matrix polymer ((AP/EP) blend) contained 70 vol.% of EP. At I center dot a parts per thousand currency signaEuro parts per thousand 35 vol.% at T a parts per thousand currency signaEuro parts per thousand 80A degrees C, where the suspensions were in sol state, strain-hardening behavior was observed. This strain hardening of the suspensions is attributable to the elongational flow properties of (AP/EP) medium. At critical gel state (I center dot = 35 vol.% and T = 100A degrees C) and in gel state (I center dot a parts per thousand yenaEuro parts per thousand 40 vol.%), the elongational viscosity exhibited the strain-softening behavior. These results strongly suggest that the strain softening results from the strain-induced disruption of the network structure of the SiO2 particles therein.