This study was undertaken to determine the thermal properties of, and the pyrolysis products from, western cottonwood (Populus trichocavya) and two of its major components: cellulose and xylan. The modifications due to treatment of the wood and its components with an acid and alkali were also documented. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA), as well as direct pyrolysis into a temperature-programed gas-liquid chromatograph, were used in this investigation. The components of cottonwood were found to generally behave the same in a thermal environment, both in isolated form and when combined in the whole wood. The hemicellulose, xylan, was completely pyrolyzed prior to the onset of cellulose pyrolysis. The acid salt treatment decreased pyrolysis rate of wood, cellulose, and xylan, and increased char, water, and furan compounds while decreasing the major two and three carbon fragments. The alkali treatment also decreased the pyrolysis rate and increased the production of char and water, but decreased the furan compounds while increasing the two and three carbon fragments.