Abstract: Objective: To explore the relationship between integral cognitive level and gray matter volume in Alzheimer's disease (AD). Methods: 20 AD patients, 17 MCI patients and 12 healthy old persons were in this study.All subjects were examined by T1-3 D BRAVO (brain volume) sequence in 1.5 T magnetic resonance scanner. The volume of gray matter was measured with Voxel-based morphometry (VBM). All subjects were underwent MMSE and obtained the score of MMSE. The multiple regression analysis of gray matter volume were compared with MMSE score. Receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of gray matter volume in AD. Results: All of the subjects with reduced gray matter volume of brain, also reduce the MMSE score, gray matter volume decreased by 10 m L and MMSE score decreased by 0.56 points (P<0.01). The decline was more pronounced in men and in younger groups. The area under the curve (AUC) of the gray matter volume was 0.927. The optimum threshold was 538.49 m L, the specificity was 90.0% and the sensitivity was 84.6%. Conclusion: As the volume of gray matter decreased, the level of integral cognition also decreased. The gray matter volume in all patients and control group could reflect the integral cognitive level. The measurement of gray matter volume in the brain could provide valuable information for the diagnosis of AD.