The effects of 15 inorganic and organic acid potassium salts on hydrothermal decomposition of glucose, fructose and 5-hydroxymethylfurfural (5-HMF) were investigated at 180 degrees C. The rate constants for glucose, fructose and 5-HMF decomposition with anions were calculated by a pseudo first-order equation, and the impact factors of the rate constants were calculated, to demonstrate the catalytic effect of the different anions. Compared to the results without added salts, chloride, bromide, iodide and nitrate anions did not significantly accelerate the decomposition rate of glucose or improve the selectivity for 5-HMF, but increased the decomposition rate of fructose from 19% to 44%, and improved the selectivity for 5-HMF by 4-29%. Phosphate, fluoride, sulfate and all organic acid anions increased the decomposition rate of glucose and fructose by 23-2781%, but lowered the selectivity for 5-HMF from 36% to 100% as compared to the results without added salts. These findings provide insights on the reactivity and mechanism of the hydrothermal decomposition of glucose and fructose with inorganic and organic salts. (C) 2012 Elsevier Ltd. All rights reserved.