The correlation between chemical structure and mesomorphic properties is one of the most important problems in liquid crystals science. 3,5-Disubstituted 1,2,4-oxadiazoles are very convenient model-compounds for studying the dependence of the LC properties on the molecular design. The transition temperatures and dielectric properties of 1,2,4-oxadiazoles depend significantly both on the position of the substituents with respect to the heterocycle and on their donor or acceptor features.