Although P300 activity have been widely investigated in dementia of Alzheimer’s type (DAT), there have been relatively few number of studies investigating P300 topography. In order to evaluate significance of changes in topography of P300 activity, we prospectively studied 23 patients with DAT and 15 healthy controls. Changes in latency, amplitude and topography of P300 activity were detected with P300 mapping, which was elicited by standard auditory oddball paradigm and recorded from the 10-20 system electrod localizations with linked-ears reference. P300 latencies were significantly longer (434.2±63.3 msec) than controls. P300 amplitudes were not significantly different from controls. Topographically, P300 activity was most prominent in the parieto-central region in controls, whereas it was more anteriorly localized in 8 of 23 patients with DAT. However, this anteriorization observed on mapping did not reach statistical significance, probably because of limited number of subjects. We concluded that the topographical evaluation of P300 activity may contribute to detect the cognitive functioning in DAT.