MgF2 single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. To control the presence of oxygen impurity, it was first suggested to measure the ionic conductivity in MgF2 crystals by impedance spectroscopy. The characteristics of ionic conductivity of “as grown” (i.e., without thermal treatment) crystals and crystals obtained by commercial vacuum technology practically coincide: the volume conductivity σv = 1.4 × 10−7 S/cm at 773 K and the ion-transport activation energy E a = 1.40 ± 0.05 eV. Annealing MgF2 crystals during electrophysical studies upon heating from 293 to 823 K in vacuum (residual pressure ∼1 Pa) for 4 h led to their partial pyrohydrolisis. The influence of this thermal treatment of MgF2 crystals on their optical transmission is studied in the wavelength range of 115–300 nm.