Abstract: Conversion of cellulose and starch to furfural was investigated over four zeolites. The zeolites were characterized by X-ray diffraction, ²⁷Al MAS NMR, IR spectra of pyridine adsorption and NH₃ temperature-programmed desorption. The roles of acidity and pore structure of zeolites in conversion of cellulose and starch were discussed in detail. The results showed that Hβ zeolite with appropriate Brønsted acid sites, Lewis acid sites and pore structure was effective to produce furfural from cellulose and starch. HY zeolite could not catalyze cellulose reaction with high conversion because of its weak acidity. However, HY zeolite was effective to produce 5-hydroxymethylfurfural (HMF) from starch. H-mordenite and HZSM-5 zeolites with fewer Lewis acid sites could not cause the isomerization reaction from glucose to fructose. So, the further conversion of fructose to furfural or HMF was inhibited. The formation of HMF only depended on the acid properties of zeolites. The formation of furfural was not only determined by the acidity of zeolites, but also by their appropriate pore structure.