The molecular dynamics and local structure in the alpha and beta phases of CD3CN were studied by H-2 NMR spectroscopy. From the NMR spin-lattice relaxation time (T-1), the activation energies of the rotation of the CD3 group about the C-3 axis in both phases were found to be 6.2 and 11 kJ mol(-1), respectively. These activation energy values suggest that the packing between CD3CN molecules in the a phase is weaker than that in the beta phase. The slow structural change of the crystal due to the alpha-beta phase transition was investigated using the H-2 NMR spectra and T-1. A jump of CH3CN between two neighboring sites in the hydrogen-bond network accompanying the molecular reorientation was observed by the H-2 NMR 2D exchange spectra and the stimulated-echo method in the cc phase. Vacancy diffusion occurred in the one-dimensional hydrogen-bond network in the alpha phase.