A batch-type subcritical water system was used to perform the decomposition reaction Of D-fructose to 5-hydroxyrnethy furfural (HMF) over a temperature range of 473-593 K. The catalytic effect of various organic and inorganic acids with pH values in the range of 1.5-5 was evaluated. It was found that not only the pH, but also the nature of the acids, had great influence oil the decomposition pathway. At lower pH, rehydration of HMF to levulinic and formic acids occurred, whereas at higher pH. polymerization reactions occurred. Phosphoric acid (pH 2) was determined to give good balance between activity, yield, and byproduct amounts. The optimum condition for the best yield of HMF (65%) was achieved at a temperature of 513 K for a residence time of 120 s. The decomposition reaction of other monosaccharides and disaccharides were also investigated, and it was determined that the ketohexoses give higher yields than aldohexoses. However, all saccharides showed the possibility of the conversion to HMF in subcritical water.