Novel mesogenic para-substituted dibenzo-18-crown-6 (I a-c) and dibenzo-24-crown-8 (II d, e) are studied. Synthesis and the structural investigations of 4,4'(5')-bis(4''- alkoxybenzylidenamino)-dibenzo-18-crown-6 (I-a), 4,5'-bis (3''-(4''-alkoxyphenyl-)-3''-oxo-1''-propenyl-amino)- dibenzo-18-crown-6(I-c), 4,5'-bis(4''-(4'''- alkoxybenzoyloxy)-benzylidenamino)-(II-e) are presented. The high temperature nematic phase is observed for the trans- isomers of materials I-b,c and II-d,e. The aroylvinylamine- derivatives (I-c, II-e) have higher phase transition temperatures than relevant azomethine derivatives (I-b, II- d). Among studied compounds the material II-d is the most stable. Materials I and II have also rather complex solid state polymorphism. The structure of Cr-8 (II-d and II-e) was investigated by the x-ray scattering method. In crystal phases of II-d and II-e the monoclinic lattices have been found with a equals 5.48 angstrom, b equals 8.34 angstrom, c equals 47.3 angstrom (beta) equals 124 degrees and a equals 45.0 angstrom, b equals 8.8 angstrom, c equals 13.8 angstrom, (gamma) equals 111 degrees parameters, respectively. The conformation of a central crown-ether fragment in the crystal as well as in nematic phase is suggested.