Objective To explore the effect of serum testosterone level on the pathologically aggressive behavior and the synaptic plasticity in the prefrontal cortex of puberty rats after gonadectomy. Methods Thirty male rats, 21 days old, were randomly divided into 3 groups: gonadectomized group, model group and control group. The gonadectomized and model groups were given a series of standard stress from 21 days old to puberty to induce animal model of pathological aggressive behavior. Resident-intruder experiment was performed to observe the variation of aggressive behaviors of animals. Enzyme-linked immunosorbent assay was used to examine the serum testosterone level. Western blotting analysis was used to determine the expression of postsynaptics density-95 (PSD-95) and growth associated protein-43 (GAP-43) in the prefrontal cortex. Results Resident-intruder experiment showed that the latency to the first attack in the gonadectomized group decreased significantly (P<0.01,P<0.01) and the attack times after yield increased significantly compared with those in the other two groups (P<0.01,P<0.01). The serum testosterone in the gonadectomized group was significantly decreased compared with the other two groups as shown by ELISA results (P<0.01, P<0.01). In addition, the aggressive-related behavior indices had a moderate to high negative correlation with the testosterone level (P<0.01). Western blotting analysis showed that prefrontal cortex expression of PSD-95 and GAP-43 in the gonadectomized group was significantly lower than those in the other two groups(P<0.01, P<0.01). Conclusion Low serum testosterone level can cause damage to the neuroplasticity of prefrontal cortex in puberty rats, which might be related to the pathologically aggressive behavior.