Both evidences of cognitive and functional impairments are necessary for the diagnosis of dementia. Following instruments: Mini-Mental State Examination (MMSE), Blessed Dementia Scale (BDS) and Hasegawa Dementia Scale (HDS) for cognitive assessment, and Activity of Daily Living (ADL) and Pffefer's Social Function Questionnaire (POD) for function measurement, were used in a survey sample of 5055 aged persons. It was found that the scores of both categories of tests were significantly correlated. The scores of MMSE, BDS and HDS were highly education-related, thus the education-dependent cutoff point should be decided. Among the cognitive assessment scales, MMSE and HDS seems better than BDS, while in functional scales, POD was more suitable for community survey. Sensory and motor disturbances, emotional and health problem were also interfered with both cognitive and daily or social function, it should be taken account in the diagnostic process for dementia.