Lignin is one of the main components of the pulping liquors and a potential source of high-added-value chemicals. The aim of this work is to evaluate the potential of industrial Eucalyptus globulus sulfite liquor and kraft liquors (collected at different stages of processing before the recovery boiler) for the production of syringaldehyde (Sy) and vanillin (V) by oxidation with O2 in alkaline medium. Oxidations were performed in a jacketed reactor with controlled temperature and pressure by (1) direct reaction of pulping liquors and (2) reaction of kraft lignins isolated from liquors. Lignins produced by LignoBoost technology were also evaluated. The products profiles were established, as well as the yields, temperature and O2 uptake during the reaction. Sulfite liquor is the best raw material leading to the highest yield by direct oxidation (33 kg of Sy and 15 kg of V per lignin ton), followed by thin kraft liquor (KL) which, compared to evaporated and heat treated liquors, also led to lower proportion o...