Aim: In this study we used the Nelson’s Modified Card Sorting Test (MCST) to find the differences between Alzheimer’s disease (AD) group/Vascular dementia (VD) group and a normal control group (non-dementia and non-AD), and to identify the commonality between the MCST and dementia patients. Patients and Methods: The MCST was administered to 32 AD patients, 18 vascular dementia patients, and 38 controls. The relationship between the MCST performance and demographic characteristics was evaluated. Results: There were no statistical differences in age, sex, level of education, smoking, drinking and depression in the three groups. The MCST was classified into four groups for analysis—number of categories completed (Cat), preservative error score (PE), non-preservative error score (NPE), unique error (UE) and total error (TE). For Cat, UE and TE showed a significant difference in all three groups, whereas PE and NPE revealed no significant difference. Conclusion: These findings suggest that cognitive function appears to significantly impair MCST performances in AD and VD patients, so these should be taken into consideration during an interpretation of the clinical assessment. For the effective use of the MCST in a clinical setting, further studies of specific clinical populations are planned to develop normative data for elderly Taiwanese people.