Objective To observe the changes of intracellular free calcium and the expression of CaM in the hippocampal neurons of posttraumatic stress disorder (PTSD) rats and to further investigate the neurobiological mechanisms. Methods The SPS-method was used to set up the rat PTSD models. A total of sixty male Wistar rats were randomly divided into 12 hours,1 day,4 days,7 days groups of SPS and normal control group. The intracellular free calcium was examined by fluorescence spectrophotometer. The expression of CaM was detected by using immunohistochemistry, Western blotting and RT-PCR. Results The intracellular free calcium level in the hippocampus of experimental rats was markedly increased 12 hours after SPS stimulation,and reached the peak after 1 day, then gradually decreased to normal level after 7 days. The expression of CaM in the hippocampus 1day after SPS was also the highest and then gradually decreased.Conclusion The lasting dysfunction of CaSUP>2+/SUP>CaM signaling cascades in hippocampal may play important roles in the pathogenesis of PTSD rats.