1. The effect of dynamic pressures with amplitudes extending from 65 to 1800 kbar on two modifications of niobium pentoxide, T−Nb2O5 and H−Nb2O5, has been studied. It is shown that shock compression can effect transitions in either direction. 2. A model of the phase transitions of niobium pentoxide subjected to dynamic pressures and residual temperatures in preservation experiments is proposed. 3. It is found that the shock hugoniot of porous (ρ00 = 3.09 g/cm3) H−Nb2O5, like those of porous glass, marble, and magnesium oxide, is characterized by anomalies that cannot yet be satisfactorily explained.