ObjectiveTo investigate the expression and activity of p38 mitogen-activated protein kinase (p38 MAPK)in hippocampus CA1 and CA3 area of rats with conditioned fear.Methods 24 h after rat model of conditioned fear was established,rats were sacrificed,then expression of p38 MAPK and phosphorylated p38 MAPK (Thr180/Tyr182) in hippocampus CA1 and CA3 area of rats were detected by western blot.ResultsCompared with control group ( ratios of value of gray scale were 1.0 ± 0.1 and 1.0 ± 0.2,respectively),expression of p38 MAPK and phosphorylated p38 MAPK (Thr180/Tyr182) in hippocarpus CA1 area of rats with conditioned fear (9.4 ± 2.6 and 7.8 ± 2.1,respectively) were significantly increased ( n =9,P ＜ 0.05 ).Compared with control group ( 2.1 ± 0.5 and 1.4 ± 0.5,respectively),expression of p38 MAPK and phosphorylated p38 MAPK (Thr180/Tyr182 ) in hippocampus CA3 area of rats with conditioned fear (6.2 ± 3.3 and 2.6 ± 0.6,respectively)were also significantly increased ( n =9,P ＜ 0.05 ).Conclusionp38 MAPK may play important role in the formation of long term memory of conditioned fear.