The propagation of undamped transverse thermal waves in a layer of binary mixture is investigated. It is shown that when the thermal diffusivityKTis equal to the mass diffusivityKS, such waves do not exist. But whenKT>KS, these waves may exist provided the layer is heated from below (such that thermohaline instability does not occur) and the concentration of the solute in the mixture decreases vertically upward. The analysis also reveals the interesting result that whenKT<KS, undamped waves can propagate even if the layer is heated from above provided the concentration increases vertically upward. It is further shown that as in a homogeneous fluid, weakly damped low‐frequency waves can propagate and the regions in the parameter space where such propagation is possible are delineated. High‐frequency waves are shown to be always strongly damped.