Mesoporous Nb2O5nH2O was prepared using amphiphilic block copolymers (L64, P103, and P123) that acted as structure-directing agents. The pore size in the prepared materials increased with increasing molecular weight of the block copolymer at the same weight percentage of ethylene oxide groups in the following order: P123 > P103 > L64. The obtained samples had BET surface areas of 250-350 m2 g -1 and pore volumes of 0.2-0.4 mL g-1, which are larger than that of bulk Nb2O5·nH2O. Fourier transform-infrared (FT-IR) analysis using CO and pyridine as basic probe molecules indicated no significant differences in the acid strength of the Lewis and BrØnsted acid sites among mesoporous, supermicroporous, and bulk Nb2O5·nH2O. Mesoporous Nb 2O5·nH2O exhibits much higher catalytic activity for the hydrolysis of cellobiose than supermicroporous and bulk ·nH2O. However, no significant difference was observed between the activity of bulk and mesoporous Nb2O5·nH 2O samples for Friedel-Crafts alkylation. The results suggest that mesopores consisting of hydrophilic niobium oxide are advantageous for hydrophilic reactions, but not hydrophobic reactions.