A series of NbOx.ZrO2 catalysts containing up to 2.67 wt% Nb (ca. 80% nominal surface coverage) was prepared by incipient wetness impregnation from niobium oxalate and oxalic acid solution. The structure of the catalysts was monitored by X-ray diffraction and Raman spectroscopy. The results indicated the presence of a surface Nb phase. No evidence for the formation of crystalline Nb2O5 species was found. The development of the acidity as a function of Nb loading was monitored by adsorption of a basic probe molecule followed by infrared spectroscopy. The results indicated the appearance of Bronsted acid sites for a threshold of Nb loading. The abundance of Bronsted acid sites correlated well with the isopropanol dehydration activity. The overall behavior was very similar to that reported earlier for the WOx/ZrO2 system.