Background: Senile plaque is one of the main pathological features in Alzheimer's disease (AD). beta-amyloid (Aβ) deposition forms the core of senile plaques, and Aβ 25 - 35 is now recognized as a neurotoxic segment. Aβ protein precursor (APP) 319-335 segment (APP 17-mer peptide) has neurotrophic and neuro-protective effects. Objective: To illustrate the effect of APP 17-mer peptide on the neurotoxicity of Aβ. Design: A standard controlled study. Setting and materials: The study was made in the Department of Neurobiochemisty, Xuanwu Hospital of Capital University of Medical Sciences. SY5Y cell line is a gift of Karolinska Institute in Sweden. APP 17-mer peptide and Aβ 25 - 35 were synthesized by means of solid phase method, and purified by high performance liquid chromatography (HPLC). Methods: APP 17-mer peptide and Aβ 25 - 35 were synthesized by solid phase method and purified by HPLC. Human neuroblastoma cells SY5Y were grouped into normal control group, Aβ 25 - 35 damaged group and Aβ 25 - 35 + APP 17-mer peptide for neuroprotection group. Cell count, MTT metabolic rate, lactate dehydrogenase(LDH) leakage rate, axonal length, area of cell body, and concentration of intracellular free calcium ion were used as indicators. Results: Compared with the normal control group, Aβ 25 - 35 reduced the cell count [on day 6 after inoculation, (8.39 ± 1.31) × 10 7 L -1 ] and MTT metabolic rate, increased LDH leakage rate, diminished the axonal length (35.74 ± 16.25) and the area of cell body (495.92 ± 87.68), and increased the concentration of intracellular free calcium ion, while the addition of APP 17-mer peptide normalized the foregoing changes. Conclusion: APP 17-mer peptide has neurotrophic and neuroprotective effect in alleviating the neurotoxicity of Aβ.