Abstract: A wet oxidizing process for waste soda to attain stable cooling and complete gas-liquid separation of waste soda which is discharged from a wet oxidation reactor for alkali waste liquid, and which process comprises the steps of (1) and (2) and optionally any one of steps (3) to (5), wherein (1) a wet oxidation step in which the alkali waste liquid is brought into contact with excess molecular oxygen, said alkali waste liquid being obtained by bringing an aqueous alkali into contact with a hydrocarbon fluid containing acidic substances of hydrogen sulfide and carbon dioxide, (2) a reducing step to reduce the pressure of a mixture of the oxidized alkali waste liquid from said wet oxidation step and a surplus gas, (3) a separation step to separate said mixture into a gas phase and a liquid phase in a gas-liquid separation tank, (4) a cooling step to cool the separated liquid phase and (5) another cooling step to cool the separated gas phase.