Abstract 2-(p-Substituted phenyl)-5-alkyl-1,3-dithianes, new liquid crystals, were synthesized by the thioacetalization of the corresponding aldehydes and dithiols. These compounds have characteristic supercooling states, exhibit monotropic liquid crystal phases even in the case of long terminal alkyl substituents. The mesomorphic characteristics of these compounds were different from those of the corresponding 1,3-dioxanes, this must originate in the difference in the molecular width caused by the difference in the atomic volume between sulfur and oxygen.