Aim: It is difficult to distinguish Alzheimer disease(AD) from vascular dementia(VD) clinically sometimes. The aim of this study is to investigate the differentiating utility of clock drawing test(CDT), so as to provide a measuring tool which is simple and easy to distinguish AD and VD. Methods: A total of 30 AD patients and 24 VD patients were selected from Department of Neurology, Xuanwu Hospital during August 2002 to December 2003, and those with serious lesions of vision and audition, acute cerebrovascular disease and infection of central nervous system were excluded. The CLOX method was used to examine CDT blindly by two independent neurological doctors. All the patients were visited twice after 2 weeks by the same doctor, and the correlation analysis was performed between CDT and mini-mental state examination(MMSE). Results: There were no significant differences between AD and VD patients in terms of demographic characteristics(age, gender, education) and MMSE scores. The Spearman correlation coefficient of inter-rater and intra-rater reliability were 0.91 to 0.96, and most of the correlation coefficient with MMSE and other scales were above 0.80. With the application of the Spearman correlation, only CLOX1 score, CLOX21 score and pointer subscore were significantly different between mild and moderate AD and VD groups (mild: P = 0.004, P = 0.008, P = 0.001; moderate: P = 0.020, P < 0.001, P = 0.015, respectively), while the P value of CLOX2 and other two subscores were over 0.05. Conclusion: CLOX are valid and reliable when used to screen dementia. CLOX1, CLOX21 and pointer subscore can be used to differentiate AD from VD.