Objective:To evaluate the diagnostic potential of cerebrospinal fluid ( CSF) levels of β-amyloid protein (Aβ) as biochemical marker for senile dementia in clinical practice. Methods: Sensitive enzyme-linked immunosorbent assay ( ELISA) was performed in our laboratory to detect the CSF levels of Aβ1-40, Aβ1-42 in 54 patients with Alzheimer's disease (AD), and 30 normal controls (NC). Results: The cut off value of Aβ ratio and Aβ1-42 concentration in NC group provided 54. 51％, 90. 00％ sensitivity and 81. 25％, 84. 38％ specificity respectively in diagnosis of AD. Conclusion: AD group bad a significant decreased level of Aβ1-42 and an increased level of Aβ ratio, compared with NC group.