To investigate the correlation between the event related potentials (ERPs) and evaluation of Montreal Cognitive Assessment (MoCA). Methods The cognitive function of aged people was evaluated by MoCA. Then ERPs data revelant to audio oddball paradigm in participants were recorded and analyzed. The regression analysis was applied to investigate the relationships of the MoCA score with latency and amplitudes of ERPs components. Results The MMN and P3a components of ERPs were recorded in all the participants. No correlation was found between MMN and the score of MoCA (p > 0.05). There was a negative correlation between P3a latency and MoCA (p = 0.000). A negative correlation between P3a amplitude and MoCA was found (p = 0.009). Conclusions The P3a component of ERPs can be used as an objective index to examine the cognitive function of aged people.