A new series of thermotropic liquid-crystalline poly (ester-β-sulfide)s (HQH-n) was prepared which contained the p-phenylene di (p-oxybenzoate) (HQH) unit. The thermodynamic parameters of the nematic-isotropic melt phase transition were analyzed in terms of the number n of methylene groups in the sulfide spacer segment (n = 2 to 10). It is found that the flexible segment behaves principally as a diluent of the mesogen, in contrast with previously studied poly (ester-β-sulfide)s containing different mesogenic groups.