A compact process based on a gas/liquid contactor was designed for the continuous alkaline oxidation of xylose into lactic acid. An experimental design using Doehlert’s method was used to study the effect of : i) the NaOH concentration, ii) the xylose concentration, iii) the reaction temperature, and iv) the residence time, on the yield of lactic acid. Results indicate that the conversion of xylose at concentrations between 5-15% (w/w) is complete and nearly instantaneous at both high temperatures (over 200 degrees C) and high sodium hydroxide concentrations ((> 10% w/w). Yields of lactic acid reaching 50% (with a theoretical yield of 60% (w/w)) were obtained under the most favorable experimental condition suggested by the model developed.