Functionalized silica nanoparticles with strong acidity and different hydrophobicity were successfully synthesized by an alkali co-condensation method. The structure of the hydrophobic solid acids were characterized, and the catalytic properties were investigated in fructose dehydration to 5-hydroxymethylfurfural (5-HMF). Experiment results indicated that catalyst hydrophobicity has a positive influence on both 5-HMF yield and selectivity. The highest yield of 5-HMF (87%) with full conversion of fructose was obtained when the most hydrophobic solid acid (SiNP-SO3H-C-16) was used as the catalyst. The reason can be interpreted as the hydrophobic groups in the silica nanoparticles can effectively isolate-SO3H groups with water molecules in the reaction system, and thus hinder the rehydration of 5-HMF, which is the main side -reaction in 5-HMF formation. Other important reaction parameters such as reaction medium, temperature, time and catalyst loading were also studied for fructose dehydration. Recycling and control experiments demonstrated the good reusability and stability of the functionalized silica nanoparticles. Furthermore, inulin was also used as a feedstock for 5-HMF production and gave a high 5-HMF yield of 65% in the catalysis of a moderate hydrophobic silica nanoparticle. (C) 2016 Elsevier B.V. All rights reserved.