The present study aimed to investigate the effects of humanin (HN) on primary cortical neuronal apoptosis induced by Abeta31-35, and explore the potential mechanisms. Cultured cortical neurons were pretreated with different concentrations of HN (5, 10, 20 micromol/L) for different time period (0, 8 and 16 h) respectively, and then exposed to Abeta31-35 (25 micromol/L) for additional 24 h and the neuronal apoptosis was examined by morphological analysis, flow cytometric assays and TUNEL staining. Caspase activities were measured using a spectrophotometer. Bax expression was measured by Western blot. The results were as follows. (1) Pretreatment with HN (20 micromol/L) for 16 h significantly prevented Abeta31-35-induced apoptosis in cortical neurons; (2) HN significantly decreased Abeta31-35-induced elevation of caspase-3 and -9 activities; (3) HN suppressed Abeta31-35-induced translocation of Bax from the cytosol to mitochondria, but had no effect on overall Bax expression. In conclusions, HN attenuated Abeta31-35-induced cortical neuronal apoptosis by blocking intrinsic caspase-dependent apoptotic pathways.