By means of plane-wave pseudopotential techniques we have computed the electronic and the vibrational properties of Hf 1− x Ge x O 2 alloy as a function of Ge concentration in the range 0.0≤ x≤ 0.5. By effect of Ge doping the tetragonal distorted fluorite structure, that for zero doping at ambient condition is meta-stable with respect to the monoclinic phase, decreases its energy by effect of doping and becomes energetically favoured at moderate doping concentration. At the same time the c axis of this phase decreases approaching the value of cubic symmetry at about x~ 0.13. The average of the main component of the dielectric constant decreases as a function of doping up to moderate Ge concentration at which the cubic phase is stabilized by Ge doping; the dielectric constant of this structure (κ~ 20) is larger than the one of bulk monoclinic HfO2, but lower than the one predicted of bulk undoped cubic system.