Objective To determine the characteristics of early cognitive dysfunction and N300 event-related potentials(ERPs)in patients with acute cerebral infarction(ACI).Methods Thirty patients with ACI and thirty normal healthy elderly people were studied.The two groups were examined with a picture recognition test and EEG waveforms were recorded.The ERPs were analysed statistically.The mini-mental state examination(MMSE) was used to evaluate cognitive function,and the results were correlated with the ERPs. Results The average MMSE scores of the ACI and control groups were significantly different.Reaction times(RTs)in the picture recognition test were(798.63±49.32)ms in the ACI group and(765.21±35.67)ms in the control group,a difference significant at the 5% confidence level.The average accuracy rates,(59.75±8.45)%and(65.26±9.28)%,were also significantly different.Average N300 ERPs the in the ACI group were significantly lower than those in the control group,and the average latencies were significantly longer.Both latency and amplitude in the ACI group showed a linear correlation with MMSE scores. Conclusion The ERPs of ACI patients have some clinical significance,and can be used as a scale-based assessment of cognitive function.