Polymer and rubber materials show remarkable nonlinear viscoelasticity. The nonlinearity may be due to change in material structures, i.e. entanglement and filler structures. The way of thinking leads us to make simultaneous measurements of the responses to large stimuli and additional responses to perturbative stimuli, i.e. differential dynamic modulus and volume resistivity. It has been found that nonlinear viscoelastic properties of entanglement and filler dispersed polymeric systems originate with ruptures in entanglement and filler networks. Rheology gives us extremely effective tool to detect such change in various network structures.