Objective To analyze the characteristics of P300 event-related potential (ERP) in rural patients with mild cognitive impairment (MCI) and to provide a method for improved early diagnosis of MCI among rural residents.Methods Thirty-five MCI patients (MCI group) and 32 healthy elderly residents without marked cognitive impairment (control group) were selected from the rural areas in Weifang City, China from December 2010 to May 2012. To evaluate the cognitive function of these subjects, mini-mental state examination (MMSE) was used, and the P300 ERPs of both groups were recorded with a passive auditory oddball paradigm using the ESI-64 system (Neuroscan Inc., USA) that is used for collecting and recording EEG signals.Results After adjustment for such factors as sex, age, and educational level, the MMSE score showed a significant difference between the two groups (P<0.01). Compared with the control group, the MCI group had a significantly prolonged P300 latency (P<0.01) and a reduced, but not statistically significant, P300 amplitude (P>0.05).Conclusions Measurement of auditory P300 ERP latency, not limited by language or text, is particularly suitable for quantitative evaluation of the cognitive function among the elderly in rural areas. It holds promise for noninvasive diagnosis and evaluation of MCI among the elderly in rural areas.