Synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), is widely considered as one of the major mechanisms underlying learning and memory. This study explored hippocampal synaptic plasticity and spatial memory formation of an Alzheimer's disease (AD) rat model established by intrahippocampal injection of oligomeric Aβ(1-42). Twenty four Sprague-Dawley rats at 2.5 months of age were randomly divided into AD and control groups, and were bilaterally injected with 5 μg oligomeric Aβ(1-42) or normal saline into dentate gyrus (DG) of hippocampus. Morris water maze test was used to observe the capability of learning and memory of two groups, 30 d after injection. To investigate the variations of paired-pulse facilitation (PPF) and range of synaptic plasticity, field potentials were recorded in the DG of the dorsal hippocampus by stimulating the perforant path (PP). The results showed that oligomeric Aβ(1-42) obviously impaired spatial memory formation in rats (P < 0.05). Furthermore, oligomeric Aβ(1-42) reduced the PPF ratio (P < 0.05) and hippocampal LTP formation (P < 0.05), while facilitated the hippocampal LTD formation (P < 0.05). These data suggest that chronic Aβ aggregation impairs synaptic plasticity of hippocampal PP-DG pathway, which may be involved in the spatial memory deficit in AD rats.