Ketone bodies, D-beta-hydroxybutyrate and acetoacetate, produced by the metabolism of fatty acids, are an important energy source for many organs, especially the heart, kidney and brain. They are utilized by the body with the help of succinyl CoA transferase (SCOT), which is ubiquitously expressed in various organs. Previously, we identified a novel SCOT-t specifically expressed in testicular germ cells and sperm, substituting somatic cell-type SCOT, however the physiological role of SCOT-t had not then been clarified. In the present study, we investigated the effects of ketone bodies, the substrate of SCOT-t, on the motility and acrosome reaction of mouse sperm. D-beta-hydroxybutyrate and acetoacetate both stimulated the motility of sperm as glucose or pyruvate. The glycolysis inhibitor stopped the motility of sperm mediated by glucose but not by D-beta-hydroxybutyrate. In contrast, ketone bodies did not stimulate the activation of the acrosome reaction of sperm, different from the effect of glucose. These results indicate that ketone bodies could be involved in sperm movement but not the acrosome reaction and the SCOT-t enzyme we have identified in sperm mitochondria may have important roles in the activity of sperm, resulting in male infertility when its function is disabled.