[en] The results are given of measuring density and viscosity of melted binary mixtures NaI-CsF and NaF-CsI. The density of the melts has been measured by the method of hydrostatic weighing. Viscosity has been measured by the method of pendulum torsional vibrations; the pendulum is a platinum ball immersed into the melt in a platinum crucible. The analytical expressions of temperature dependence of density and viscosity of the melts under study are given. A change pattern of these properties with alternating composition are explained proceeding from the mode of complex structure of melted alkaline metal halogenides and their mixtures