Purpose: It has been challenging to detect early changes preceding seizure onset in patients with epilepsy. This study investigated the preictal discharges (PIDs) by intracranial electroencephalogram of 11 seizures from 7 patients with mesial temporal lobe epilepsy. Methods: The EEG segments consisting of 30 seconds before ictal onset and 5 seconds after ictal onset were selected for analysis. After PID detection, the amplitude and interval were measured. According to the timing of PID onset, the 30-second period preceding seizure onset was divided into two stages: before PID stage and PID stage. The autocorrelation coefficients during the two stages were calculated and compared. Results: Preictal discharge amplitude progressively increased, while PID interval gradually decreased toward seizure onset. The autocorrelation coefficients of PID channels were significantly higher during PID stage than before PID stage. There was an overlap between channels with PIDs and seizure onset channels (80.77%). Conclusions: Preictal discharges emerge prior to ictal event, with a dynamic change and a spatial correlation with seizure onset zone. These findings deepen our understanding of seizure generation and help early prediction and localization of seizure onset zone.