Wet air oxidation is a candidate technique for the effective treatment of wastewater contaminated by nitrogenous organic pollutants. Piperazine (PZ) is a cyclic diamine representing this class of compounds. In the present work, the wet oxidation reaction of PZ was studied for the first time. It was found that, in the studied range of temperatures of 180 degrees-230 degrees C and O2 partial pressures of 0.69-2.07MPa, the oxidation process was slow. Total organic carbon (TOC) conversion at 230 degrees C and 0.69MPa O2 partial pressure was just 52% after 2h. The investigated reaction was accelerated by a heterogeneous Ru/TiO2 catalyst. Maximum TOC conversion (91%) was achieved during catalytic wet oxidation at 210 degrees C and 1.38MPa O2 pressure. Kinetic data were collected over the range of temperatures 180 degrees-210 degrees C, O2 partial pressures 0.34-1.38MPa, and catalyst loading 0.11-0.66kg/m3. The lumped TOC concentration decay was a two-step first-order process.