The catalytic conversion of microcrystalline cellulose is examined over a niobic acid catalyst (NBO) prepared by an alkali fusion method. The catalytic activity of NBO is significantly affected by the reaction conditions and further acid treatment. The highest 5-hydroxymethylfurfural (HMF) yield of 7.0 mol % and a glucose yield of 17.7 mol % at a cellulose conversion of 54.2% are achieved at 230 degrees C for 2 h. The H2SO4-treated (NBS) and H3PO4-treated (NBP) samples both show greatly improved performance over NBO due to the introduction of strong acid sites and the increase in specific surface area. NBS gives a glucose yield of 26.0 mol % and an HMF yield of 14.1 mol %, while NBP exhibits a glucose yield of 21.4 mol % and an HMF yield of 15.5 mol %. NBO shows excellent recyclability for the catalytic hydrolysis of cellulose. The recovered NBS and NBP samples can be regenerated by calcination and subsequent acid treatment.