Sulfonated graphene oxide (SGO) is a promising solid acid catalyst for many acid-catalyzed reactions, but its synthesis typically requires complicated post-functionalization. Herein, a one-pot method was developed to directly synthesize SGO. Characterizations showed that the SGO has abundant acid sites, including SO₃H (1.62 mmol g⁻¹), OH and COOH, and a two-dimensional (2D) structure. An efficient reaction system using SGO as a solid acid catalyst was developed for the dehydration of fructose into 5-hydroxymethylfurfural (HMF). A high yield of HMF up to 94% was obtained with a low loading of SGO. Moreover, the SGO is also capable of converting high-concentration fructose (20 wt%) with an acceptable yield of 67%. The high catalytic activity was attributed to the abundant active sites and the 2D structure which enhances the accessibility of the active sites.