The viscosities of molten alkali fluorides (LiF, NaF, KF, RbF, and CsF) were measured at temperatures 373.15K above the melting point. The viscosity has been measured by using a high-temperature oscillating viscometer modified so as to be able to determine the period and logarithmic decrement from the observed intervals between times when the oscillation passes two deflection angles and automatically calculate the viscosity. The data obtained were discussed in terms of viscous flow theory in ionic liquids. New data regarding the configurational changes in alkali fluoride ionic melts were obtained.