SUMMARYThe relationship between the computerized EEG data and the mental function was studied in 73 subjects aged 60 and over in a home for the aged. The mental function was examined by Hasegawa Test (HT) (simplified dementia rating scale) and Bender Gestalt Test (BGT), and the degree of the mental deterioration was classified as normal, sub‐normal, pre‐dementia, dementia of HT, and as (‐), (+), (++), (+++) of BGT. The EEG records were analyzed quantitatively at resting state with eye‐closed and also at eye‐opened state. EEG variables were compared in each group of the two tests and the both states. The following results were obtained.1) EEG variables correlated more closely with the score of BGT than that of HT in general.2) The percent time alpha and alpha continuity at the eye‐closed state decreased significantly in dementia group of HT and (+++) group of BGT.3) With the progress of the deterioration of BGT, the percent time alpha at the eye‐opened state gradually increased, and the ratio of the percent time alpha at the eye‐opened state to the eye‐closed state increased lineally.4) With the progress of the deterioration of BGT, the percent time theta increased gradually, and the number of theta waves over the amplitude of 30 μV increased lineally especially in the central area at eye‐closed state.5) By eye opening the number of theta waves over 30 μV decreased significantly in (‐) and (+) groups of BGT, but did not change in (++) and (+++) groups.6) The peak frequency and the percent time beta did not correlate with the mental function in the aged.Parts of this paper were presented at the 5th Annual Meeting of Japan EEG and EMG Society, Tokyo, December, 1975 and at the 6th Annu