This study is concerned with the synthesis and characterization of two new series 3-(4-pentoxyphenyl)-5-(4´-substituted phenyl)-1,2,4-oxadiazole and 3-(4-pentoxy benzoyloxyphenyl)-5-(4´-alkoxy benzoyloxy phenyl)-1,2,4-oxadiazole of fifteen new compounds. The first series 3-(4-pentoxyphenyl)-5-(4´-substituted phenyl)-1,2,4-oxadiazole of ten compounds with the structural formula This was prepared as following: at first by reaction of p-hydroxy benzaldehyde (1) with hydroxyl amine hydrochloride to give p-hydroxy benzaldoxime (2) which then dehydrated by acetic anhydride to give p-hydroxy benzonitrile (3). Alkylation of compound (3) give p-pentoxy benzonitrile (4) and this compound react with hydroxyl amine hydrochloride to give 4-petoxy benzamidoxime (5) which finally react with p-substituted benzoyl chloride to give 3-(4-pentoxyphenyl)-5-(4´-substituted phenyl)-1,2,4-oxadiazole (6)a-j. The second series 3-(4-pentoxy benzoyloxyphenyl)-5-(4´-alkoxy benzoyloxyphenyl)-1,2,4-oxadiazole includes five compounds, , with the structural formula This was prepared as following: p-hydroxy benzonitrile (3) react with p-pentoxy benzoyl chloride to give of p-pentoxy benzoyloxy benzonitrile (7) this compound reacted with hydroxylamine hydrochloride to give p-pentoxy benzoyloxy benzamidoxime (8) than finally reacted with p-alkoxy benzoyloxy benzoyl chloride to give 3-(4-pentoxy benzoyloxyphenyl)-5-(4´-alkoxy benzoyloxyphenyl)-1,2,4-oxadiazole (11)a-e. All the synthesized compounds were characterized by FTIR spectroscopy. The compounds 3-(4-pentoxy phenyl)-5-(4´-butoxy phenyl)-1,2,4-oxadiazole, 3-(4-pentoxy phenyl)-5-(4´-chlorophenyl)-1,2,4-oxadiazole , 3-(4-pentoxy benzoyloxy phenyl)-5-(4´butoxy benzoyloxy phenyl)-1,2,4-oxadiazole and 3,5-(4,4- pentoxy benzoyloxy phenyl)-1,2,4-oxadiazole were also characterized by 1HNMR. The liquid crystalline behaviors of the two series have been examined by means of hot-stage polarizing microscopy for the determination of phase transition temperatures and the type of mesophases. Microscopic observations of first series compounds at liquid crystalline transition temperature displayed a nematic mesophase of typical nematic droplets are observed on cooling from the isotropic liquid for compounds 3-(4-pentoxy phenyl)-5-(4´-propoxy phenyl)-1,2,4-oxadiazole (6)c, 3-(4-pentoxy phenyl)-5-(4´-butoxy phenyl)-1,2,4-oxadiazole (6)d and 3-(4-pentoxy phenyl)-5-(4´-pentoxy phenyl)-1,2,4-oxadiazole (6)e , while compounds 3-(4-pentoxy phenyl)-5-(4´-methoxy phenyl)-1,2,4-oxadiazole (6)a and 3-(4-pentoxy phenyl)-5-(4´-ethoxy phenyl)-1,2,4-oxadiazole (6)b did not show any liquid crystalline properties. Compounds 3-(4-pentoxy phenyl)-5-(4´-floro phenyl)-1,2,4-oxadiazole (6)f and 3-(4-pentoxy phenyl)-5-(4´-iodo phenyl)-1,2,4-oxadiazole (6)i also did not show any mesomorphic properties, while compounds 3-(4-pentoxy phenyl)-5-(4´-chloro phenyl)-1,2,4-oxadiazole (6)g and 3-(4-pentoxy phenyl)-5-(4´-bromo phenyl)-1,2,4-oxadiazole (6)h show a nematic droplets mesophase. Compound 3-(4-pentoxy phenyl)-5-(4´-nitro phenyl)-1,2,4-oxadiazole (6)j shows monotropic smectic A and nematic phases. Liquid crystalline properties of compounds 3-(4-pentoxy benzoyloxy phenyl)-5-(4´-alkoxy benzoyloxyphenyl)-1,2,4-oxadiazole showed a nematic mesophase of a typical droplet texture.