BACKGROUND & AIMS: Esketamine, a promising treatment for treatment-resistant depression, has shown potential advantages over traditional antidepressants. However, its mechanisms remain unclear. This study explores how esketamine alleviates depressive behaviors through activation of the BDNF/TrkB/PI3K/AKT signaling pathway. METHODS: Using a Chronic Unpredictable Mild Stress (CUMS) rat model, behavioral assays (Sucrose Preference Test, Morris Water Maze Test) and histological analyses (HE and Nissl's staining) were performed. Esketamine (5 mg/kg) treatment was administered to evaluate its antidepressant effects, and the PI3K inhibitor, PI3K-IN-6, was used to investigate the role of the PI3K/AKT pathway in the underlying mechanism. RESULTS: Esketamine treatment improved depressive behaviors, enhanced neuronal structure, and reduced apoptosis and oxidative stress. These effects were linked to the activation of the BDNF/TrkB/PI3K/AKT pathway. PI3K-IN-6 reversed the effects, confirming the pathway's involvement. CONCLUSION: Esketamine alleviates depressive behaviors by activating the BDNF/TrkB/PI3K/AKT signaling pathway, reducing oxidative stress and inhibiting neuronal apoptosis. These findings highlight the therapeutic potential of esketamine in treating depression, particularly in cases where traditional treatments fail.