Objective:To elucidate the changes in apparent diffusion coefficients(ADC)by quantify diffusion weighted (DW)magnetic resonance imaging(MRI)in patients with Alzbeimer's disease(AD),and the relationship between micro-structure changes of white matter(WM)and the cognitive impairment thereof.Methods:The DW-MRI was performed in 30 probable AD patients and 30 normal controls with normal-appearing white matter(NAWM).The ADC was measured in different WM areas.The neurologic and neuropsychological assessments were examined with mini-mental state examination(MMSE)in patients.The ADC were determined in standard regions of the frontal,temporal,occipital and parietal white matter,genu,splenium of the corpus callosum.Results:The value of ADC was higher in frontal,splenium corpus callosum,temporal,and parietal white matter of AD group than that of control(P ＜ 0.01).There was no significant difference in the ADC value of genu and occipital white matter between AD and control groups(P＞ 0.05).The score of MMSE was 24.1±0.8 in AD group.The ADC values of parietal,splenium of the corpus callosum and frontal white matter were significantly negatively correlated with MMSE scores in AD group(P ＜ 0.05 or P ＜ 0.01).There was no correlation between the ADC values of genu of the corpus eallosum,temporal and occipital white matter with the MMSE score(P ＞ 0.05).Conclusion:The quantitative DWI analysis of MRI DWI may be helpful in assessing WM abnormalities in AD.The parietal WM abnormalities may play an important role in the development of dementia.It was showed that Alzheimer's cognitive decline with ADC value and micro-structure of white matter was closely related.