Biomass can be converted to liquid product for fuels and for chemicals by hydrothermal treatment. A method for further treatment of the liquid product much depends on the composition determination, and therefore analysis of the liquid product is important. The much water makes the analysis difficult, while much pretreatment will make the analysis complicated and bring more error sources. Herein hydrothermal treatment of cellulose was carried out, and the liquid product was directly analyzed by GC/MS. The major components were identified as some small acids, ketones, some five ring oxygen-containing compounds, and small amounts of some phenol derivatives. Specially, the content of the major component of levulinic acid in two reaction systems are compared, and the effect of the water solvent on the levulinic acid content is discussed. Phenol in the product is specially analyzed by MS/MS mode for assurance, and the result confirms the existence of phenol in the liquid product by hydrothermal treatment of cellulose. (C) 2011 Elsevier Ltd. All rights reserved.