The effects of TiO2 (anatase TiO2 or rutile Ti02) and ZrO2 (monoclinic/tetragonal mixture ZrO2) on glucose and fructose reactions were examined in hot-compressed water at 473 K with a batch type reactor. Rutile TiO2 (r-TiO2) is inactive during glucose reactions. A monoclinic/ tetragonal mixture of ZrO2 (m/c-ZrO2) was the basic catalyst for the reaction at this temperature. Anatase TiO2 (a-TiO2) showed both acidity and basicity during the reactions. In order to understand the catalytic activity of a-TiO2, r-TiO2, and m/c-ZrO2, we measured the acidity and basicity by means of NH3- and CO2-TPD, respectively. The TPD analysis showed us that the amount of acid (670 mu mol/g) and base (550 p,mol/g) sites on m/c-ZrO2 were the highest among these three catalysts, while the density of acid site (17 mu mol/m(2)) and that of basic site (9 mu mol/m(2)) of the a-TiO2 were the highest. Such the acidity and basicity analyses suggested that the amount of basicity was the key factor for the isomerization while the density of acidity and basicity was important for the HMF formation from glucose. (c) 2005 Elsevier B.V. All rights reserved.