Objective To explore the protective effects of Caspase inhibitor on in vitro hippocampal neurons of rats with oxygen glucose deprivation (OGD) injury.Methods The primary hippocampal neurons from newborn Sprague-Dawley rats were cultured for 7 days,and then,divided into control group,OGD/re-OG treatment group,Caspase inhibitor (Z-VAD-FMK) treatment group and DMSO treatment group; and OGD/re-OG was performed in the later three groups for OGD duration of 6 h.Through the experimental process,20 μmol/L Z-VAD-FMK was given to the Z-VAD-FMK treatment group,while 1‰ DMSO was added into culture medium in the DMSO group.The morphology of the neurons was observed 24 hours after re-OG under light microscopy and electron microscopy.MTT assay was used to determine the rate of survived cells and lactate dehydrogenase (LDH) content in culture medium.The neurons apoptosis rate was measured by using flow cytometry (Annexin V-FITC/PI).Caspase-3 activity of neurons was analyzed by colorimetry.The protein expression of Caspase-3 wasassessed by Western blotting.Results Cells in the OGD/re-OG treatment group showed swelled body,some having ruptured membrane,cell integrity being damaged,cell nucleus edema,mitochondrial swelling and cristae ordered chaos; cells in the Z-VAD-FMK treatment group showed decreased injury as compared with the OGD/re-OG treatment group,having cell integrity; as compared with the OGD/re-OG treatment group,Z-VAD-FMK treatment group had significantly higher absorbance value (0.204±0.019 vs.0.303±0.018) and cell survivalrate (0.481％±0.045％vs.0.704％±0.040％),obviously decreased lactate dehydrogenase (LDH) content ([406.500±21.286] U/L vs.[326.000±20.278] U/L),apoptosis rate (49.700％±3.100％ vs.29.820％±2.839％),absorbance value of the Caspase-3 active area and Caspase-3 protein expression (1.070±0.077 vs.0.785±0.058),with statistically differences (P＜0.05).Conclusions Caspase inhibitor may protect rat hippocampal neurons from oxygen glucose deprivation injury by inhibiting Caspase-3 activity.