Objective To observe the changes of phosphorylated extracellular signalregulated kinase 1/2 (pERK1/2) and EM>c-fos/EM> in the medial prefrontal cortex (mPFC) of post-traumatic stress disorder (PTSD) rats. Methods Male Wistar rats were randomly divided into control group and PTSD model group. The model group rats were exposed to the singleprolonged stress (SPS) to set up the rat PTSD model. The expression of pERK1/2 was detected using immunohistochemistry and Western blotting, and the expression of EM>c-fos/EM> mRNA was detected using reverse transcriptionpolymerase chain reaction (RT-PCR). Results The result of immunohistochemistry analysis showed that the number of pERK1/2-positive cells of control group and model group were 10.4±2.07 and 48.8±10.08 respectively （EM>P/EM><0.01）, and integral optical density were 24.955±3.691 and 110.810±10.643 respectively （EM>P/EM><0.01）. And Western blotting showed that relative expression quantities of pERK/βactin were 0.510±0.052 and 1.109±0.106