The paper reports the determination of the times of the orientational relaxation of a succinonitrile trans isomer in the plastic and liquid phase in the temperature range from 292.3 to 348.9 K, by the depolarized Rayleigh light scattering method. The activation energy of the process of the trans isomer reorientation in the plastic phase was found to be 11.6+/-4.2 kJ/mol. The decay constants of the interaction-induced processes in the liquid and plastic phase as well as the squares of the effective anisotropy of the optical polarizability of both trans and gauche isomers and the anisotropy due to the interaction-induced processes were determined.