A model study of the influence of an entrainment separator on the efficiency of a molecular (short-path) distillation was performed. The temperature of the entrainment separator was determined from the balance equations for a one-dimensional model of molecular distillation. The initial period of distillation was investigated by using the direct simulation Monte Carlo method. The study of stream flows in an evaporator for a two-dimensional model of molecular distillation was also performed. The obtained results indicate that a sieve in the distillation gap of a molecular evaporator, acting as an entrainment separator, improves the composition of the distillate, although it also decreases the distillation rate. This effect is especially valuable when there is splashing, i.e., physical transfer of distilled liquid from the evaporator to the condenser. Hence, such a sieve stabilizes the distillate composition and muffles the effect of splashing.