Poly[4-(4-hydroxyphenoxy)benzoic acid] was prepared by the bulk polycondensation of 4-(4-acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350-degrees-C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with XnBAR of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide-angle X-ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300-degrees-C and 410-degrees-C, respectively. The polymers with low molecular weights showed nematic textures above 300-degrees-C. This nematic/isotropic phase transition temperature is lower than that of poly(4-hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain.