To compare the neuropsychological impairment between patients with early-onset and late-onset Alzheimer's disease (AD). Methods: Total 137 patients diagnosed with probable AD in the department of Neurology of Tongji Hospital were recruited from October 2018 to October 2020, including 65 cases with early-onset (onset age less than 65 years old) Alzheimer's disease (EOAD group), and 72 cases with late-onset Alzheimer's disease (LOAD group). A series of neuropsychological tests including Mini-Mental State Examination (MMSE), Clock Drawing Test (CDT), Boston Naming Test (BNT-30), Activity of Daily Living Scale (ADL), and Neuropsychiatric Inventory (NPI) were performed for all patients. Demographic and neuropsychological data were compared between these two groups of patients. Results: MMSE score of the EOAD group were significantly lower than that of the LOAD group (P=0.009). CDT, BNT-30, ADL, total NPI, and caregiver distress scores showed no significant differences between the two groups. The sub-scores of depression and apathy of the EOAD group were higher than those of the LOAD group (P=0.030, P=0.035), while apathy was significantly more common in the EOAD group than the LOAD group (52.31% v.s. 33.33% , P= 0.025). The total NPI score of the EOAD group was negatively correlated with MMSE, CDT, and BNT-30 scores, and was positively correlated with ADL score, while that of the LOAD patients was only positively correlated with ADL score. Caregiver distress score was positively correlated with NPI total scores in both groups. Conclusion: Patterns of neuropsychological impairment were different between the EOAD and the LOAD patients with higher degrees of cognitive decline, depression, and apathy in the EOAD patients.