Biomass continues to be an important candidate as a renewable resource for energy, chemicals, and feedstock. Decomposition of biomass in high temperature liquid water is a promising technique for producing industrially important chemicals such as 5-hydroxymethylfurfural (5-HMF), furfural, levulinic acid with high efficiency. Hexose, which is the hydrolysis product of cellulose, will be one of the most important starting chemicals in the coming society that is highly dependent on biomass. Taking fructose as a model compound its decomposition kinetics in organic acids-enriched high temperature, liquid water was studied in the temperature range from 180 degrees C to 220 degrees C under the pressure of 10 MPa to further improve reaction rate and selectivity of the decomposition reactions. The results showed that the reaction rate is greatly enhanced with the addition of organic acids, especially formic acid. The effects of temperature, residence time, organic acids and their concentrations on the conversion of fructose and yield of 5-HMF were investigated. The evaluated apparent activation energies of fructose decomposition are 126.8 +/- 3.3 kJ mol(-1) without any catalyst, 112.0 +/- 13.7 kJ mol(-1) catalyzed with formic acid, and 125.6 +/- 3.8 kJ mol(-1) catalyzed with acetic acid, respectively, which shows no significant difference. (C) 2009 Elsevier Ltd. All rights reserved.