Non-Gaussian diffusion showed the potential to advance the understanding of microstructure alternation in Alzheimer’s disease (AD). Apparent Diffusion Coefficient at Ultrahigh b-values (ADC_uh) demonstrated improved sensitivity to white matter degeneration in AD. In this study we compared the quantitative change of diffusion characteristics including conventional ADC, Diffusion Kurtosis Imaging (DKI), and ADC_uh. Moreover the correlation between diffusion characteristic and cognitive impairment was investigated. The results of this pilot study showed a close link between ADC_uh in left thalamus and cognitive impairment in AD patients. But further study with larger sample size is required to draw a clear conclusion.