Abstract The present study was aimed to treat the synthetic pulping liquor (COD = 5120–15,360 mg/l) by non-catalytic wet oxidation (WO) process at medium temperature and pressure conditions (130–170 °C and 0.12–0.55 MPa, respectively). The laboratory scale reaction was carried out in a high pressure reactor with a working wastewater volume of 300 ml for 4 h duration. The maximum COD and color removal were 55% and 70%, respectively at 170 °C temperature and 0.37 MPa oxygen partial pressure. After the treatment, the biodegradability of the wastewater was increased to 0.66 from an initial value of 0.22. The COD data with time at different temperatures were fairly fit in second order kinetic model and the activation energy of the reaction was calculated as 76.5 kJ/mol. From the study, it was suggested that the non-catalytic WO process can be sufficient to make the wastewater amenable to biological oxidation thus eliminating the problems related to catalyst recovery and regeneration.