We report the synthesis and characterization of a new polymorph (β) of HfMo₂O₈. This phase is synthe-sized from the trigonal (α) HfMo₂O₈ by application of high pressures and high temperatures. The sample obtained is characterized by powder x-ray diffraction (XRD) and the details of high-pressure and high-temperature phase are explained. The Rietveld analysis of the powder XRD data reveals that the β=HfMo₂O₈ crystallizes in a monoclinic lattice with unit cell parameters a=11.4138 (6),b=7.9105(4),^_c=7.4395(3), Ȧ and β=122.35(0)^°. The β-HfMo₂O₈ is found to be isostructural to the room-temperature phase of b-ZrMo₂O₈. The coordination numbers of Hf and Mo atoms with oxygen atoms are eight and five, respectively. The nature and sharing of Hf and Mo polyhedra are entirely different in β modification compared to that in the α phase.