Cyclic olefin copolymer (COC, poly(norbornene-co-ethylene) catalyzed by ansa-ethylenebis-(indenyl)zirconium dichloride (Et[Ind]2ZrCl2)/methylaluminoxane (MAO) gives rise to phenomenal increase of Tg upon annealing. Unaveraged solid-state 13C NMR resonance of the CH carbons in the norbornene (53 and 49 ppm) evidenced the conformation conversion from T[X]T and G[X]G to more stable T[X]G conformers (where [X] = [T] or [G] represent the norbornene chain conformation). As the persistent length increases with the conversion, local packing of the rigid chain subsequently occurs. Synchrotron source X-ray diffraction provides clear evidence of the averaged interchain contraction from 12.0 to 8.5 angstrom and a tighter distribution in the spacing after annealing. In the preannealed state, T1pH relaxation time revealed both mobile (where conformer converts) and rigid components (where conformation is frozen), which coalesce into a further rigid component after extended annealing. The mechanisms governing the packing in amorphous COC are likely by the random chain diffusion and not from cooperative motion as described by the bundle-packing model.