Objective To observe the expressions of Caspase-9,Caspase-3, cytochrome C and their relationships, and investigate apoptotic mechanisms in hippocampus of posttraumatic stress disorder(PTSD) rats. Methods Sixty male Wistar rats were used in the present study. The singleprolonged stress (SPS)method was used to set up the rat PTSD models. There were six groups：after SPS 1 day，4 days，7 days，14 days，28 days groups and control group. The expressions of Caspase-9, Caspase-3 and Cytochrome C proteins were detected with immunohistochemistry, immunofluorescence and Western blotting. Results Immunohistochemical and immunofluorescent results showed that the expression of cytochrome C peaked at 4 days and maintained higher level at 7days after SPS. Expressions of Caspase-9 and Caspase-3 were increased and peaked at 7days after SPS. Western blotting results showed that compared with control group, cytochrome C protein was upregulated and peaked at 4 days after SPS in the cytosol. Compared with the control group, cytochrome C tended to decrease in mitochondrial fractions. The activated form of Caspase-9 and Caspase-3 were not detected in control group. They were pres