Mitochondrial dysfunction plays a key role in the pathogenesis of depression. Ample research proves mitochondria are a promising target for depression. Fibroblast growth factor 21 (FGF21) exerts roles in neuroprotection and could enhance mitochondria function. Here, the anti-depressive effect of FGF21 was evaluated on a chronic unpredictable mild stress (CUMS)- induced model of depression. The depressive-like behaviors were assessed using sucrose preference test (SPT), forced swim test (FST) and tail suspension test (TST). The results showed that treatment of FGF21 significantly attenuated the decrease in SPT, and dramatically reduced the immobility time in the TST and FST. These effects were associated with enhanced hippocampal mitochondrial function, reflected by FGF21-induced increases in mitochondrial ATP concentration, mitochondrial membrane potential (MMP), and decrease of reactive oxygen species (ROS) levels. At the same time, FGF21 ameliorated oxidative stress in CUMS-exposed mice by enhancing superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase activities, and reducing malondialdehyde (MDA) level in the hippocampus. Mechanistically, we found that CUMS treatment decreased expression level of mitochondrial fusion protein 1 (MFN1), and increased expression level of mitochondrial dynamin-related protein 1 (DRP1). FGF21 administration increased expression of MFN1, and reduced expression of DRP1. Meanwhile, FGF21 treatment promoted the expression levels of Nrf2, HO-1, phosphorylated AMPK, SirT1, PGC-1a in the hippocampus. This study revealed that FGF21 alleviates CUMS induced depressive like behaviors by restoring mitochondria function via enhancing Nrf2/HO-1 and AMPK/SirT1/PGC-1α signaling pathways. It suggested that FGF21 would be a potential therapeutic agent in the management of depression.