According to previous reports, the oxidative dehydrogenation of lactic acid to pyruvic acid in an aqueous phase does not proceed with Pd/C, while Pd/C doped with Te or Pb has catalytic activity at atmospheric pressure and 363 K in an aqueous NaOH solution at a pH of 8. Since use of heavy metals, such as Te or Pb, is inconsistent with green chemistry, a heavy-metal-free Pd/C catalyst is employed in the present study. The oxidative dehydrogenation of sodium lactate to sodium pyruvate in an aqueous phase at 358 K under pressurized oxygen at 1MPa proceeded favorably using Pd/C with no adjustment of solution pH. Under pressurized oxygen, the catalytic activity of Pd/C was similar to that of Pd/C doped with either Te or Pb. This result suggests that a heavy-metal-free Pd/C catalytst might also be applied to other catalytic reactions. As an alternative to doping Pd/C with Te or Pb, the dissolution of gaseous oxygen into the reaction solution significantly enhanced the catalytic activity of Pd/C. To show the contribution of the dissolution of gaseous oxygen, the effects of the volume of oxygen in the reactor (stainless autoclave) on the reaction rate and the activity were examined. The activation parameters thus obtained reveal that the volume of oxygen in the reactor is a more important determinant of catalytic activity than the activation of the reaction itself.