Intracellular accumulation of abnormally phosphorylated tau in different types of neurons is a pathological characteristic of Alzheimer's disease (AD). While tau modification and associated neuronal loss and hypometabolism start in the entorhinal cortex (EC) in early AD patients, the mechanism by which mutant P301L hTau leads to dementia is not fully elucidated. Here, we studied the effects of P301L hTau transduction in the medial EC (MEC) of mice on tau phosphorylation and accumulation, and cognitive deficit. We found that the exogenous mutant tau protein was restricted in MEC without spreading to other brain regions at one month after transduction. Interestingly, expression of the mutant tau in MEC induces endogenous tau hyperphosphorylation and accumulation in hippocampus and cortex, and inhibits neuronal activity with attenuated PP-DG synapse plasticity, leading to hippocampus-dependent memory deficit with intact olfactory function. These findings suggest a novel neuropathological mechanism of early AD, which is initiated by tau accumulation in MEC, and demonstrate a tau pathological model of early stage AD.