CO 2 gas dissociation through optical and plasma collision breakdown was investigated by optical emission spectroscopy (OES), using an Andor Mechelle monochromator with an iStar intensified charge coupled device (ICCD). A pulsed Nd:YAG laser was used to provide energy for the gas breakdown processes. The evolution of the luminous plasmas was examined by time-resolved optical spectroscopy. Emission lines of carbon and oxygen species, such as atomic C (I), ionic C (II) and atomic O (I), were observed to understand the process of CO 2 dissociation. Effects of background gas pressure on plasma propagation in the experiments were studied. Some emission lines could be obviously distinguished, indicating that the emitting species had different behaviors in the evolution. They were frequently ionized and excited after the laser irradiation.