Objective To explore the effects of dihydrostestosterone(DHT) on synaptic plasticity and the expression of N-methyl-D-aspartate receptor 1（NMDAR1） in CA1 region of hippocampus in senescence accelerated mouse prone strain 8(SAMP8). Methods Twenty-one 6-month-old male SAMP8 were randomly divided into sham-operation control group, castrated group and DHT replacement therapy after castration group（7 in each group）. The dose of DHT was 1mg/(kgI>&#/I>8226;d) . Twentyone days later, the apical dendritic thorns density in hippocampal CA1 region was observed with Golgi staining method. Immunohistochemical method and computer pathological image analysis system were used to determine the expression of synaptophysin and N-methyl-D-aspartate 1(NMDAR1) in hippocampal CA1 region. Results 1. In the Golgi staining, the number of the apical dendritic thorns density of hippocampal CA1 region of castrated group decreased. However, DHT replacement therapy could significantly increase the apical dendritic thorns density (EM>P/EM><0.05). 2. The expressions of synaptophysin and NMDAR1 in the hippocampal CA1 region of castrated group decreased markedly. The average absorbance (AEM>A/EM>) values were sharply lower than those of other groups (EM>P/EM><0.05). DHT replacement therapy could obviously increase the expression of synaptophysin and NMDAR1 in the hippocampal CA1 region. Conclusion DHT replacement therapy can increase the density of dendritic thorns and modulate synaptic plasticity of hippocampal CA1 region. DHT may potentially affect hippocampal synaptic