2H NMR measurements on carbon-black-filled&crosslinked polybutadiene (PB) networks and unfilled counterpart reveal the strong uniaxial-elongation dependence of both the transverse relaxation rate (1/T 2) and the splitting distance (Δν) of NMR lineshape; furthermore, the fluctuating part, instead of the static residual part, of quadrupolar interaction is found to govern the transverse relaxation signal at large deformation ratios (e.g., λ extt1.5) or high filler loads (e.g., 25phr or higher). The comparison of the T 2's or Δν's in both unfilled and filled cases and in the cases of different λ ext's indicates that in filled cases, the rubber matrix does not undergo overstrain in a wide range of λ ext, and chain breakage is prevented. This is also supported by the environmental scanning electron microscopy evidence for the deformation of carbon black clusters/network. In contrast, the unfilled PB network tends to undergo inhomogeneous deformation as λ ext increases, as confirmed by more than one 2H NMR doublets.