Silver nanoparticles (Ag-np) are very promising engineered nanomaterials which play an important role in the world biomedical, healthcare and in general nanotechnology applications. With the most impressive effect in antibacterial and many other broad-spectrum biotechnological advantages, Ag-np in real applications is still a controversial issue. This study investigated effects of the Ag-np on hippocampal synaptic plasticity and spatial cognition in rats and followed with the research on their possible mechanism. In this study, twenty-four adult male Wister rats were randomly divided into 3 groups: control group, low-dose group (Ag-np, 3. mg/kg) and high-dose group (Ag-np, 30. mg/kg). After two-week exposure to Ag-np through the nasal administration, Morris water maze (MWM) test was performed for the spatial cognition, followed by the long-term potentiation (LTP) recording and reactive oxygen species (ROS) detection in hippocampal homogenate. Results showed that compared with the control group, both LTP and MWM were abnormal in low-dose group and high-dose group. The quantity of ROS in hippocampal homogenate was increased significantly in low-dose group and high-dose group, which may be the reason of the neural damage caused by Ag-np.