Objective:To investigate the effect of melatonin (MT) on hypoxia-induced injury of PC12 cells and its mechanism.Methods:PC12 cells cultured in vitro were divided into the control, the hypoxic, and three groups of hypoxic cells combined with different doses (low, medium, and high) of MT at 12.5, 25, and 50 μmol/L, respectively. Cell viability was measured by MTT. The expression of cysteine-containing aspartate 3 (cleaved caspase-3) and SOX2 proteins was detected by Western blot. The expression of SOX2 mRNA was detected by real-time fluorescence quantitative polymerase chain reaction (PCR). The activity of superoxide dismutase (SOD) and content of malondialdehyde (MDA) were detected by the kit. The combined treatment group with the most significant effect was selected as the hypoxia+MT group, and then the effects of hypoxia+MT, hypoxia+siRNA-NC, hypoxia+siRNA-SOX2, hypoxia+MT+pcDNA, and hypoxia+MT+pcDNA-SOX2 on cell viability, apoptosis, protein expression level of cleaved-caspase-3, protein and mRNA levels of SOX2, SOD activity, and MDA levels, respectively, were investigated.Results:Compared with the control group, cell survival rate and SOD activity in the hypoxia group were significantly decreased, while cell apoptosis rate, cleaved caspase-3 protein expression level, MDA content, SOX2 mRNA, and protein expression level were significantly increased (all P<0.05). The effects of low, medium, and high levels of MT and the low expression of SOX2 could ameliorate the above changes induced by hypoxia (all P<0.05), while the overexpression of SOX2 could alleviate the effects of MT on the viability, apoptosis, and oxidative stress of hypoxia-induced PC12 cells (all P<0.05). Conclusions:MT can reduce hypoxia-induced injury to PC12 cells by inhibiting the expression of SOX2.