Objective To explore the effect of androgen on learning and memory ability and neurons in hippocampal CA1 region in senescence accelerated mouse prone strain/8(SAMP8). Methods Thirty 7monthold male SAMP8 were randomly divided into shamoperation control group, castrated group and androgen replacement therapy after castration group. The dose of testosterone undecanoate (TU) was 37.4mg/(kgI>&#/I>8226;15d). The capability of learning and memory was observed 45 days later through the Morris water maze(MWM) test and the change of neurons in hippocampal CA1 region was detected and analyzed by HE staining，immunohistochemal method and computer pathological image analysis system. Results 1. In the MWM test, the escape latency of castrated group were significantly prolonged(P<0.05).And the times of spanning flat roof decreased(P<0.05). Testosterone replacement therapy can improve the learning and memory ability. There was no significant difference from shamoperation control group(P＞0.05). 2. With HE staining, neurons in hippocampal CA1 region of castrated group were found with diffused vacuolar degeneration, and sparse and disordered cellular arranpement. The cell nucleuses were karyochrome and karyopycnosis. The number and optical density of Aβ immune positive neurons were markedly higher than those of other groups(P<0.05). Conclusions Androgen deficiency after castraton results in the decreased learning and memory ability and injury in hippocampal neurons.Andr