Deficiency of the Caenorhabditis elegans protein, DIC-1, located in the inner membrane of mitochondria produces an abnormal mitochondrial morphology. The mechanism by which DIC-1 controls the topology of the inner membrane was investigated by transiently over-expressing DIC-1 in C. elegans. Cryo-electron microscopy showed that DIC-1 over-expression greatly increased the number and fractional area of mitochondrial cristae, suggesting that DIC-1 actively participates in cristae formation. These morphological changes were accompanied by increases in the oxygen consumption rate and ATP content of C. elegans worms, and decreases in reactive oxygen species (ROS) and sensitivity to paraquat. DIC-1 knockdown induced the opposite changes in ATP, ROS and paraquat-sensitivity. The ability of DIC-1 to increase cristae formation and secondarily, oxidative phosphorylation, suggests a potential use of this factor to control mitochondrial activity.