Objective To investigate the protective effect of β-hydroxybutyrate (BHB) against hypoxic injury in neurons of Sprague-Dawley (SD) rats and related mechanism.Methods Primary cultured neurons of SD rats were pretreated with BHB at various concentrations (2 mM, 5 mM, 10 mM, 20 mM, and 50 mM) for 24 hours and then put in a tri-gas incubator for glucose-oxygen deprivation for 2 hours. A mitochondrial superoxide probe was used to examine mitochondrial oxidative stress in neurons; CCK-8 assay was used to measure the change in cell viability; QPCR was used to measure the mRNA expression of sodium-coupled monocarboxylate transporter 1 (SMCT1), caspase-3, and cytochrome C, and Western blot was used to measure the protein expression of SMCT1, caspase-3, cytochrome C, extracellular signal-regulated kinase 1/2 (ERK1/2), and phosphorylated ERK1/2 (p-ERK1/2) (T202/204).Results BHB at concentrations of 2 mM, 5 mM, and 10 mM had no significant influence on the viability of neurons (P>0.05), while BHB at concentrations of 20 mM and 50 mM caused a significant reduction in the viability of neurons (P<0.05). After hypoxic culture of the neurons, there was a significant reduction in viability (P<0.05), a significant increase in mitochondrial oxidative stress (P<0.05), significant reductions in the mRNA and protein expression of SMCT1 (P<0.05), significant increases in the mRNA and protein expression of caspase-3 and cytochrome C (P<0.05), and a significant reduction in the phosphorylation level of ERK1/2 (P<0.05). As for the hypoxic neurons pretreated with BHB, a low concentration of BHB had no significant influence on neurons (P>0.05); compared with the simple hypoxia group, the 10 mM-BHB group had a significant improvement in the viability of neurons (P<0.05), a significant reduction in mitochondrial oxidative stress (P<0.05), significant increases in the mRNA and protein expression of SMCT1 (P<0.05), significant reductions in the mRNA and protein expression of caspase-3 and cytochrome C (P<0.05), and a significant increase in the phosphorylation level of ERK1/2 (P<0.05).Conclusions High concentrations (>20 mM) of BHB have a toxic effect on neurons; low concentrations (<5 mM) of BHB have no significant influence on neurons with glucose-oxygen deprivation; BHB at a concentration of 10 mM can increase the expression of SMCT1, reduce mitochondrial oxidative stress and apoptosis by activating the ERK1/2 signaling pathway, and thus exert a protective effect on primary neurons with glucose-oxygen deprivation.