The production of xylose fromEucalyptus globulus wood samples in media containing sulphuric acid was studied. The prehydrolysis reactions were carried out in autoclave. All the experiments were performed with liquid/wood ratio of 10 g/g. The effects of sulphuric acid concentration (within the range 2–6%), reaction time (0–6 h) and temperature (115 or 130°C) on the type and distribution of reaction products were studied. Xylose was the main compound generated by hydrolysis. The xylose concentration/time series of data were fitted to a kinetic model which provided a close reproduction of experimental results. The concentrations of other reaction products (glucose, arabinose, furfural and acetic acid) in reaction media were also determined. The results obtained are compared with those obtained in experiments carried out at atmospheric pressure.