Methylmalonic acidemia is an inherited metabolic disorder that leads to brain damage associated to the accumulation of methylmalonic acid (MMA) and impairment of energy metabolism. We demonstrate here that treatment with diazoxide, an agonist of mitochondrial ATP-sensitive K⁺ channels (mitoK_ATP), can prevent death promoted by treatment with MMA in PC12 cells and freshly prepared rat brain slices. This diazoxide effect was reversed by 5-hydroxydecanoate, a mitoK_ATP antagonist, confirming it occurs due to the activity of this channel. Diazoxide was not capable of preventing inner membrane potential loss promoted by MMA and Ca²⁺ in isolated mitochondria, indicating it does not directly prevent mitochondrial damage. Furthermore, diazoxide did not prevent cellular respiratory inhibition in cells treated with MMA. Interestingly, we found that the mitochondrial inner membrane potential within intact cells treated with MMA was maintained in part by the reverse activity of ATPsynthase (ATP hydrolysis), and that diazoxide prevented the formation of the membrane potential in the presence of MMA, in a manner sensitive to 5-hydroxydecanoate. Furthermore, the effects of diazoxide on cell survival after treatment with MMA were similar to those of ATPsynthase inhibitor oligomycin and adenine nucleotide translocator inhibitor atractyloside. These results indicate that diazoxide prevents PC12 cell death promoted by MMA by decreasing mitochondrial ATP hydrolysis. These results uncover new potential neuroprotective effects of mitoK_ATP agonists under situations in which oxidative phosphorylation is inhibited.