Background: The aim of this study was to investigate changes in event-related potentials (ERPs) between coma and awakening in patients with large left hemispheric infarction (left LHI). Material/Methods: Ten patients with left LHI who suffered coma and survived to awaken were enrolled in this study. The eye-opening subscore of the Glasgow Coma Scale (GCS) was used to assess the extent of patients' arousal. ERPs elicited by the passive oddball paradigm were collected during coma and awakening states, respectively. Peak latencies, peak amplitudes, topography, and time-frequency information of P1, N1, P2, and mismatch negativity (MMN) were compared between the 2 sessions. Results: No significant differences in the peak amplitudes and peak latencies of P1 and N1, but significantly greater P2 amplitude with shorter latency in left hemisphere and midline was shown in the awakening state compared with that in coma. A marked shift of P2 topography in response to deviant tones was also seen, from the right centro-parieto-frontal areas during coma to left frontal-midline areas during awakening. MMN waveforms were not detected in 6/10 patients during the coma state, but these 6 patients all recovered to awakening. Evoked oscillations in bilateral hemisphere were profoundly inhibited during the coma state, with poor inter-trial phase synchronization, while obvious activities with broader frequency ranges and consistent inter-trial phase synchronization were observed during awakening state, and different frequency activities were distributed in distinct brain regions. Conclusions: P2 may be a central index of coma recovery and a component of the arousal system. Changes in time-frequency information could provide more information during coma recovery, perhaps including some cognitive processing of the sensory stimulus.