Subcritical water is an environmentally attractive solvent for organic matters and can be used to liquefy biomass to biocrude, which is a mixture of oxygenated hydrocarbons of varying molecular weights. Liquefaction of switchgrass in subcritical water-is studied using a semicontinuous reactor in the temperature range of 235-260 degrees C. Subcritical water is pumped through a tubular reactor packed with switchgrass particles of 40-60 mesh size. The effects of reaction temperature and catalysis by K2CO3 are examined. Potassium carbonate significantly enhances the hydrolysis of macromoleculer components of switchgrass into water-soluble products. More than 50 wt % of the organic carbon available in switchgrass was converted to biocrude after 20 min of steady operation at 235 degrees C in the presence of 0.15 wt % of K2CO3. At the high temperature (260 degrees C), dehydration of biomass was favored over hydrolysis reactions. On the basis of chromatography and mass spectrometry analyses, biocrude contains lignin derived products, sugars, and its decomposition products. On the basis of the infrared spectroscopy and electron microscopy of residue solid, the subcritical water treatment causes complete breakdown of lignocellulosic structure of switchgrass. In fact, the residue solid mainly contained lignin fractions.