A detailed study of a novel synthesis via colloidal sol-gel route for obtaining nanoparticulate Nb2O5 was performed. Parameters such as temperature and H+: Nb5+ and Nb5+: H2O molar ratios were controlled in order to determine the best conditions of synthesis. Moreover, particle size distribution, zeta potential, structure by X-ray diffraction, and the photocatalytic activity of the particulate sols were also evaluated. The obtained results indicate that the colloidal sol-gel synthesis is a good alternative for obtaining Nb2O5 either as stable nanoparticulate sol or as a nanosized powder. Nb2O5 amorphous nanoparticles with an average size of 20 nm were obtained by controlling the synthesis variables. The heat-treatment process allowed the formation of Nb2O5 with orthorhombic structure that transforms at higher temperatures to monoclinic phase. The highest photocatalytic activity was observed under lambda = 365 nm, the smallest UV energy used in the experimental tests.