Abstract: Physico-chemical characteristics of steam-degraded products collected from pine-wood fiber/MPU-20 resin(polyurethanes)composites by self-designed steam injection technology and equipments were studied by experimental observation, pH value determination, FT-IR and UV-Vis spectrometries. The surfaces of wood fibers were also invesitigated by SEM microscopy during steam injection treatment. The results indicated that steam-degraded products are acidic, the pH value of which was influenced by steam pressure, injection time and retention time. FT-IR spectrum showed that steam-degraded products consist mainly of a polyoses mixture, and the produced deposites are mainly resin mixture which are structurally similar to phenol-rosin resin. SEM microscopy clearly showed some significant groove marks and sockets on the surfaces of pine wood fiber after steam injection treatment. UV-Vis spectrum suggested that acidic degraded intermediate pigments with unsaturated conjugates were probably produced from the composites by steam injection treatment. In addition, lignin molecules were also degraded or/and resolved. The compared absorbance peaks of lignin compounds showed that resin in cellulose-based composite probably reacts or combines with lignin molecules.